Fusing is the technique of joining two or more pieces of glass in a kiln by heating them to very high temperatures so they melt and stick together. In order to successfully fuse glass together, the glass must be compatible. All the glass we sell is CoE90, Bullseye compatible so you don't have to worry about this when buying or using our glass.

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Slumping is a technique that uses gravity to shape glass into the form of a pre-made mould. The glass and mould are placed in the kiln, and when the glass is heated it becomes soft and slowly drops into the mould under its own weight. This is a popular method for creating bowls and platters, but there are many other possibilities of pieces to be made using this technique.

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Tack-fusing is a process in which two or more pieces of glass are fired in a kiln at quite a low temperature, so that they just stick together but retain most of their original features. You can use this technique to retain or create texture in your pieces. See our Kiln Schedules page for a typical tack fusing schedule suitable for Bullseye Glass.

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The specific gravity of Bullseye glass is 2.5. This means that every cubic centimetre of Bullseye Glass weighs 2.5g. This is useful when calculating the weight of glass needed to fill a casting mould. Fill the mould with water, weigh the water in grams, then multiply that figure by 2.5 to calculate the weight of glass required.

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Bullseye frit comes in 5 different sizes:

Powder which has grain sizes 0.2mm and finer;
Fine which has grain sizes from 0.2mm to 1.2mm;
Medium which has grain sizes from 1.2mm to 2.7mm;
Coarse which has grain sizes from 2.7 - 5.2mm;
Extra Large (available in clear only) which has grain sizes 5.2mm - 30mm.

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Some Bullseye glass colours contain lead and cadmium, and Bullseye recommend capping these colours with clear glass if they are to be used with food. View the list of these glasses here.

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Some glass will appear very pale or even colourless in its unfired state, but when fired it will mature, or 'strike' to its target colour. Striking colours can be affected by temperature, atmosphere and the heat history of the piece, so we would recommend testing the glass before firing to make sure that the optimum target colour is reached. All striker glass styles we sell are marked as such in the product description.

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Bullseye have very specific requirements that their hand-made glass must satisfy in order to be deemed of a good enough quality to be sold as standard stock. Because of the hand-making process, inevitably some glass will not reach these requirements. This glass is classed as 'Curious' and is sold at a discounted price. Curious glass is fusible and all sheets are unique, which can make for very interesting pieces.

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During manufacture, Bullseye glass is only tested against Bullseye glass so it cannot be guaranteed to be compatible with other CoE90 glass. The only way of ensuring compatibility is to conduct your own tests. All the glass we sell is Bullseye Glass compatible.

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Glass needs to be cleaned before firing, as this removes anything that may contaminate the surface of your fired piece, such as cutting fluid, oils, dust, sticker residue or fingerprints to name just a few. These contaminants may be visible on the finished piece even if they are not visible before firing, and could cause devitrification, which is the growth of crystals on the surface of the glass. Some people ask whether fluids such as washing up liquid or hand soap, which contain detergents, are appropriate to clean glass with. These cleaning fluids are not suitable for glass cleaning, as they can cause devitrification. Our Professional Glass Cleaner is perfect for this job.

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When it is heated in a kiln to full fuse temperatures, glass naturally wants to assume a thickness of 6mm unless it is constrained by dams or a mould. This means that either 2 layers of 3mm glass, or 3 layers of 2mm glass can be stacked and the glass will not distort in the kiln. For more information, see 6mm Rule.

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Not all Bullseye glass behaves identically when heated. As different glasses have different viscosities there may be some slight variation depending on what glass you are using.

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Bullseye glass is as strong as most other glasses but is not toughened or heat resistant like Pyrex. Assuming that the glass has been annealed properly Bullseye glass can be used for placemats, plates, bowls and coasters without issue.

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Bullseye rods are given two different grades, based on their characteristics - T-grade rods, which are formulated for flameworking and are not recommended for kilnforming, and F-grade rods, which can be used for both flameworking and kilnforming. On the whole, F-grade rods behave very similarly to sheet glass, with a few differences which are mainly due to the fact that rods are thicker than the 3mm of sheet glass. View this tipsheet for more information on Bullseye rods.

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Due to the way Bullseye Glass is manufactured, your sheet may have a wavy edge. We will always aim to provide a sheet that has the surface area of the quoted dimensions. For example, if you purchase a 25cm x 20cm sheet with a wavy edge, the minimum surface area will be 500cm squared.

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If you tend to get lots of little bubble trapped between layers of glass, try sifting Bullseye Clear powder between the glass layers before firing. This actually traps more bubbles, but they are much smaller and do not attract the eye. See the Bullseye Quick Tip: Powder Power for more information.

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When using frit or stringers it’s always a good idea to run your design right to the edge of the glass, this will allow air to track out of the design instead of getting trapped and causing bubbles.

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Some bubbles are not between layers but come all the way through the glass and sometimes appear as a large hole in the glass. Large bubbles or holes in a piece are usually down to one of three things:

1. The main culprit is fusing thin glass too fast causing an 'apple pie' effect. This is where the glass seals around the edge, trapping air in the middle which then forms a bubble which turns into a hole when it pops. Use the super bubble squeeze firing schedule or use 2 layers of 3mm for the base. Bubbles in designs which use a single 3mm base with frit on top are very common and difficult to resolve without using fibre on the shelf to allow the air to track out.

2. A shelf which has been primed or has not been fired for a long time often holds moisture even though it looks dry, this moisture can turn to steam during the firing which can blow bubbles. If you get these large bubbles in a 6mm thick piece, the solution is to dry your kiln-shelf by firing it to 260C for 20 minutes with the kiln fully vented.

3. A dip in the shelf can cause bubbles, if you put a straight edge across your shelf you should not see any gaps, try this on both sides of the shelf and fire on the flattest side. Ensure that your kiln shelf has no dips in it or just flip it and use the other side.

Take a look at this video on troubleshooting bubbles:

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Bubbles with sooty deposits are usually caused by glue residue. The black is carbon left from the glue burning out. The bubble may not be where the glue originally was as it will track to the thinnest point. It’s best to avoid using glue or use it very sparingly. When glue is used, use it on the edge of the piece as this will allow it to burn away cleanly.

Take a look at this video on troubleshooting bubbles:

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You can cross-hatch stringers between layers of glass to create a pattern of small uniform bubbles. Choose a transparent glass colour, and use the same colour of stringer. Lay the stringers in a row along the base glass, and then do the same with the cap glass. Sandwich the stringers together at 90 degrees to each other before firing. This creates an elegant grid of bubbles

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Try mixing bicarbonate of soda with water, then spraying it onto the surface of the glass before capping and firing. This produces clear, random champagne bubbles in your work. The effect can be a little difficult to control, so experiment.

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This is an interesting example of how heat works in the firing. As your piece was being fired, the silver foil on top acted as a reflector, reflecting heat away from the glass beneath it and keeping it slightly cooler (and stiffer) than the surrounding uncovered glass. As the edges of the piece heated first they sealed, trapping an air bubble in the centre. In extreme situations, a fast initial ramp rate for example, this can cause the glass to crack. Interestingly this is not specific to using silver, other reflective inclusions such as dichroic, iridised and even white or light coloured opal glass, can cause the same issue. In order to combat this I would encourage using a bubble squeeze firing schedule, this slows down the heating process allowing extra time for the heat to get into the piece beneath the foil and melt the layers more evenly. Unfortunately this would only help in preventing the bubbles forming in the first place. now that they are trapped within the glass there's not much that can be done. You could fire them upside-down on a tack fuse. this would flatten the bubbles so that you have a level surface to use as a coaster. However this will give you a slightly more textured surface on this side as the glass will pick up the texture of the kiln shelf and more importantly the silver will contaminate the kiln shelf. So this would need to be done on a shelf that you don't mind contaminating.

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There are three reasons for glass cracking in the kiln:

Incompatible glass – This will only happen if you use glass from different manufacturers and is identified by the crack running around a piece of glass in the design.
Thermal shock – This is due to heating too fast or cooling too fast. Soft edges in the break indicates heating too fast and sharp edges on the break indicates cooling too fast.
Poor Annealing – Annealing should be calculated according to thickness (about 1hr for 6mm). If your design has different thicknesses the annealing hold should be doubled

For our recommended firing schedules, see our Kiln Schedules page.

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Some cracks are fixable and some are not. It depends on the crack, how severe it is and where it is on the piece. If the crack is very large or on the interior of the piece, the only thing you can really do is recast the piece, as no repair will make the crack disappear sufficiently. This is the same for thermal shock, as the edges of the crack will have rounded off, and also if your piece has stuck to the mould making material. In all of these cases, before recasting you should review your casting method and make improvements to stop the piece cracking again. If the crack is not on the interior of the piece and gluing seems appropriate, we would recommend a two-part epoxy glue such as DP460 Epoxy Glue.

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It looks like this crack was caused by thermal shock. There are a number of factors contributing to why the piece has cracked. 

Dark colours will heat up quicker than light colours, dark colours absorb heat more readily than light colours like white which will reflect heat away and heat up more slowly.
Large pieces with large areas of contrast will exaggerate this effect, the size of your piece made it difficult for the temperature between the light areas and the dark areas to be evened out.
Iridised or Dichroic coatings will also reflect heat away causing a difference in rate at which different areas will heat up.

With all three of these factors combined in your piece it was vulnerable to thermal shock. To prevent this happening on future pieces and if you re-fire this piece, I recommend slowing down your heating and cooling rates, here is a more conservative firing schedule:

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All glass will take very low as well as very high temperatures. However, as soon as glass is made into something certain things will influence how frost proof they are, especially when there are rapid changes in temperature. Things influencing the strength of glass objects are:  

• Design, variations in thickness (like a wine glass) reduces an objects ability to cope with rapid heat change.
• Poor annealing will leave permanent stress in the glass resulting in weakness which will cause the glass to crack.

If a design is even thicknesses and well annealed then it should be frost proof. To test to failure we put things in a plastic bag, freeze them overnight and then run them in the dishwasher. If they tolerate this they should survive outdoors without a problem.

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The factory cycle of your plug-in kiln may be a bit harsh if the piece was thick. Also, the piece may have gripped the mould. If the edges are sharp then the glass cracked in cooling and this would indicate either cooling too fast or gripping the mould. If the edges of the cracks are soft, then the glass had stress in it before it was fired, it was heated too fast or it was too close to the elements.  Take a look at our Successful Slumping in a Plug In Kiln tip sheet for more information, and always use the firing schedule appropriate to the specific mould, which if you bought it from us, can be downloaded from the product page for the mould.

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Devitrification or devit shows as a scummy white haze on the surface of glass after firing.  It is usually caused by contamination such as finger prints, sticker residue, grinding marks and dust. To avoid devit, clean the glass using glass cleaner and paper towel, protect the glass from dust before firing and use our basic full fuse firing schedules. If you still get devit after following these steps, try firing onto shelf primer rather than thinfire (this is essential if you have been grinding the glass).

If devitrification does occur, you can use clear powder to remove it. Take a look at this tip sheet for more information: How to Fix Surface Flaws.

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3mm Fibre is not suitable as a separator for fusing as it will stick to glass in certain circumstances. Fibre is used instead of a shelf by some people and when used in slumping will release, it can also be used in casting to form a barrier; generally opal glass will stick to fibre more than transparent glass.  The specific preparations for separating glass from the shelf are Thinfire Paper and Bullseye shelf primer.

Bullseye tip sheet about fibre paper

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Sharp edges occur on cast pieces when the glass scrapes down the sides of a casting mould during firing. To prevent this make sure that glass is positioned in the mould so that it flows out to meet the edges of the mould, rather than scraping down the sides of the mould and getting caught.

Sharp edges can be removed using various cold-working methods, ranging from using simple hand tools to using dedicated cold-working machines. We offer a range of tools suitable for all kinds of cold-work. See our hand tools and our range of cold-working machines.

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Suckers are unsightly depressions or wrinkles that can appear when casting. They are caused by differences in temperature during the cooling process, as thinner areas will cool more quickly than the rest of the piece.

To prevent suckers, keep your glass at a uniform temperature during cooling by soaking/holding the glass at 677°C to thoroughly unify the temperature, then cooling gradually to the annealing phase.

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If you grind glass prior to firing, it can cause the cut edge to devitrify on firing. This can be reduced by keeping the piece wet when grinding and cleaning the cut with a toothbrush under a running tap, this gets all the loose bits out of the cut. Then fire the piece onto shelf primer rather than thinfire as the smoke from the thinfire can help to kick off devitrification. If you fire at 333C per hour between 677C and 804C this will also help.

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Shelf primer usually only sticks if it has been fired before, it is too thick, or if the primer is very old. Outside of this, primer can stick when the firing is too high. Take a look at our Kiln Schedules page for tried and tested schedules for use with Bullseye glass. If none of these factors are the case, you can only resolve the issue by using Thinfire paper rather than shelf primer.

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Decals are a simple and effective way to add images to your glass work. They work particularly well in jewellery pieces. The firing schedule you use depends on the type of decal you have. As a general rule, decals should be applied to your finished, fired piece, and re-fired at a lower temperature to fix them permanently to the glass. Check the instructions that came with the decal or take a look at the product page for the decal you bought for instructions on how to apply and fire your particular decal.

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Different decals fire at different temperatures for optimum results, depending on the compounds within the decal. Generally if the recommended firing temperature for the decal is below tack fuse temperature then it is classed as low fire, and if it is fired at tack fuse temperatures or higher it is classed as high fire. It is usual for decals to be fired below full fuse temperature in any case. If you fire low fire decals too high they discolour and can wipe off.  High fire decals do not fix to the glass unless fired to at least 760 (tack).  See individual decals for their appropriate firing temperature. 

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If you are seeing a mark from the decal film this usually indicates that you need to use distilled water to soak your decals. Your tap water may contain a slightly higher concentration of calcium which can leave these marks. Make sure you change the water regularly if you are using lots of decals and ventilate the kiln when firing decals for the best results.

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Glassline pens are great to use like paints, you can build up lots of layers into your pieces. They can crack when they are drying out but this cracking will not affect the glass, just the look of your piece. To avoid such cracking apply the paints in thin layers. Paint one layer and let it dry then paint another layer on top. Layering up the paints also gives a good covering of colour, if you use them too thinly they can look a bit washed out after you fire them.  A good way of telling if you have enough paint down is to hold your piece up to the light and if you can see lots of light coming through it you probably need to add a bit more.

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The golden glow around the silver is silver oxide. This will always be present in silver but if you clean the silver with vinegar before use and try Crystal Clear 1401 as your clear cap you will reduce the possibility of this happening. Naturally, if you want you can get impressive reactions with glass such as French Vanilla and the reactive glasses such as Reactive Ice Clear.

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The best silver reactions happen with Red Opal, Reactive Ice and Reactive Cloud, but you can expect interesting things to happen with any glass containing sulphur as well. To find out which glasses contain sulphur just look at the check the Reactive Glass Chart.

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Both the 0.7mm and the 1mm can be used between glass and it really depends on what thickness will look best with your piece. All silver will tarnish a bit and this can be removed with Silvo or vinegar. The silver wire we sell is 999 pure and therefore will tarnish less than sterling silver. Please be aware that silver will react with some glass types, see our How To... Kilnforming Guides section for more information.

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The best way to use mica powder with glass is to use the 'painting with mica' technique, painting it onto Thinfire paper to make the mica much more controllable. Take a look at this video:

For a fine line, writing or intricate pattern work with mica, inclusion pens are excellent:

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Yes, the silver and gold flakes need to be used between layers of glass; they are made of mica and will not stick to the glass otherwise. They are a bit tricky in that they can trap a lot of bubbles. Try using them sparingly to add a little sparkle here and there.

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The Enamels we sell mature at 750 - 810C and therefore can be used in a full range of kiln work. There is no need to pre-fire before applying enamels, however the lower you fire the enamels (within the maturing range) the stronger they will come out. Pre firing layers before topping is not essential but will help to reduce potential bubbles.  Enamels do need to dry before firing or they will blister badly. Sifting a very thin layer (2 grains thick) of clear glass powder over the enamels can help achieve a smooth glossy finish and will also reduce bubbles if sifted between layers.

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Glassline paper can be fused between glass layers to add interest to your work. There is a tipsheet on how to use it here.

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Millefiori can be used on top or between layers of a fused piece. It's good to start by making some jewellery pieces and work up as you get used to the way the millefiori works with heat and class thickness. If you are placing it on top it is good to sieve a very thin layer of clear powder over the millifiori to prevent devitrification. If you are placing it between layers use our super bubble squeeze program and ensure that the design will not trap air.

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Both are used for mixing enamels for painting or printing onto glass. Water based mixing medium is an easy to use medium for mixing enamels to use for printing, with a quick drying time. It is water soluble making clean-up easy. Good for quick, one-off prints. Oil based mixing medium has a slow drying time, which is useful for mixing enamels for printing especially when printing large batches when you do not want the medium to dry in the screen for silk screen printing process. Needs to be cleaned up using white spirit as it is not water soluble. Can also be used to print onto decal paper to create your own decals.

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We have done so with success here in our studio, yes. Glass weaving and tapestry techniques rely on parallel arrangements of stringers, so if the stringers are bent, the arrangement will have small gaps which may not be desirable. The weaving technique process benefits from very straight stringer. However, as with any handmade product, there is a potential for variance. Bullseye’s latest production methods have improved straightness; but there will always be a range of acceptability. 

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Take a look at this video which demonstrates a hole being drilled in glass ready for a jewellery grommet to be fitted. This was done using a Dremel Multitool and diamond wire drill bit. Always immerse the drill bit in shallow tub of water when drilling to avoid burning off the diamonds. Risk of electricution: Always use a cordless drill or flexible shaft when using near water.

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Shelf primer (or kiln wash) is used to prevent your glass from sticking to the kiln shelf or mould during firing. We sell an number of different types and each have their particular uses:

Bullseye Shelf Primer: Our most popular kiln wash, this is a good general purpose primer. It has a helpful pink tint so you can see exactly where you have applied it (the tint burns out on firing). It also dries quickly between layers and is easy to apply evenly with a soft haik brush. Another benefit is that if you fire under 706C, then you will not need to re-apply the primer for another firing. A new coating should be applied after a full fuse (766C or higher). 

Hi-Fire Shelf Primer: An excellent shelf primer, this primer is specifically designed to perform well at high temperatures for techniques such as raking. It is also good for bead release and seems to work well at lower firing temperatures as well, making it a good all-round primer. It also has a pink tint to help show where it has been applied, and goes on nicely in even layers. It cleans from the shelf and glass easily after use.

Primo Primer: We recommend this primer for use with casting moulds, such as the Colour de Verre dragonfly mould or nano bead mould.  Although slightly more difficult to mix and apply (Tip: leave it for an hour after adding the water before mixing again and applying), it is truly excellent at releasing work from these complex moulds, leaving great detail and a smooth finish. It also needs minimal clean up afterwards.  

Boron Nitride Spray: It is expensive, but a little goes a long way and it is ideal for stainless steel moulds such as the floral former because, unlike other primers, you do not have to heat the mould for the primer to adhere. It also gives a fantastically smooth finish to your glass, minimising cold work. Not recommended for firing temperatures above product.

Bullseye Thinfire Paper: This product removes the need to prepare and apply a primer. A more expensive option than primers because the paper only lasts for one firing, but preparation times are almost zero. Just put the paper on the kiln shelf and place your work on top.  Bullseye Thinfire leaves a very smooth finish too. We use this extensively in our studio.

For more information, see the product pages or watch our YouTube video: Help Me Choose: Shelf Primers.

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Thinfire paper is a ceramic material held together with organic binders, these binders will burn between 400-600°c it is normal to notice a burning smell and even a small amount of smoke in this temperature range. After the 600°c point all of the organic material will have burnt away and the paper will have turned into a white powdery material. The appearance of the Thinfire whilst it is burning is brown and smokey, this can be alarming but it is completely normal and nothing to worry about. Take a look at this video by Bullseye Glass to see what happens to Thinfire paper during the firing cycle:  https://youtu.be/wqiYYF4SSfM 

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If you've never cut glass before, it's a good idea to take a class to teach you the basics of cutting glass, as well as the best tools and techniques to use. We also have a tip sheet on Improving Your Glass Cutting which contains some useful tips.

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The Rule of Halves refers to cutting glass. A cut is much more likely to run smoothly if there are equal amounts of glass on each side of the score, hence the Rule of 'Halves'.

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The methods used to coldwork a kilncast piece can vary depending on exactly what needs doing to the piece. If a reservoir needs removing, this can be done using a tile saw with a diamond blade, by using rotary tools, or by hand lapping with loose grit. Diamond hand tools can be used to remove small imperfections on the surface of your casting, such as flashing - areas where glass has flowed into small cracks in the mould.
Please note: A casting should be at room temperature for 24 hours before any cold work is carried out. This is because even if a piece feels cold on the outside, it could be considerably warmer in the centre, so can still be subject to thermal shock.

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Yes. Just remember to reapply primer after each firing.

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Glass and ceramic clay are not compatible. It may be possible to formulate a clay that is compatible with Bullseye glass, but as of yet this has not been achieved. Some ceramicists will incorporate glass experimentally in their pieces to create interesting effects, or for example by firing a clay pot with no base to glaze temperatures, then re-firing with glass frit in the bottom to produce a glass based pot.

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Firepolishing happens at slumping temperatures, so flat pieces can be firepolished, but more upright pieces would be affected by the heat so are not suitable to be firepolished.

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This is possible, as long as you make the correct investment mix. Castalot is an example of a great mix for creating reusable moulds.

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There are several options for glueing glass to glass, the simplest is silicone with aquarium silicone being the clearest. Single part silicone is good for glueing large areas together. Alternatively, professional laminating glues are available from Bohle and you can either use 2 part silicone glue or ultra violet curing glue, both are very strong and very expensive.

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The best product for multiple glass casting is Castalot Casting Plaster.

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Fibre paper and fibre rope are very versatile, and different thicknesses lend themselves to different tasks:

1mm fibre paper is useful for lining a box casting or for lining the base of your kiln. Some people use this fibre as a separator paper in place of kiln wash, however does not give as smooth a finish as Thinfire paper. Opal glasses tend to stick to fibre papers more than clear and transparent coloured glasses, for this reason we do not recommend fibre paper is used as a shelf separator unless it is used on combination with another separator such as Thinfire paper.

 3mm Fibre Paper is great as a separator in box casting, lining the box or protecting dams. Just cut some strips and arrange them inside the box. You can also use 3mm fibre paper to add texture to glass in a simple process known as kiln carving. It can also be used to insulate against thermal shock and improve annealing, or you can cut and construct with it for bas relief design.

6mm Fibre Paper is also very versatile. As well as kiln carving, you can cut and construct with it for bas relief design or use it to form low profile dams when making pieces using frit. Use with fibre hardener to create rigid moulds that can withstand more than one firing. 

We don’t recommend firing onto any of these fibres above 804C (for kiln carving) unless you are planning to do some coldworking.

Fibre rope can be used to create lateral holes in pendants. try using two strands of the rope to achieve a hole large enough for a necklace chain. Fibre rope can also be used in kiln carving to create shapes in glass.

To get started with kiln carving, try our Kilncarving Kit.

The fibre we sell is Biosoluble Fibre Paper. This is not the same as Ceramic Fibre (which we have never sold). The fibre paper we sell is made from an Alkaline-earth Silicate Wool, unlike Ceramic Fibre, AES Wool is bio-soluble and if inhaled does not accumulate in the lungs. This is an excellent alternative to ceramic fibre but it can be itchy so we recommend using a FFP3 Dust Mask when using this product, and cleaning up using a vacuum with a HEPA filter.

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It is simply a matter of personal taste. Some prefer the pencil grip while others like the pistol grip. We use both types regularly here at Warm Glass. For more information, take a look at our YouTube video: Help Me Choose... Glass Cutters.

Yes the fibre hardener will make the fibre hard enough to use for repeated firings. However, you will need to use Primo primer or Bullseye shelf primer on the form to allow the glass to cleanly release. You can also use iridised glass against the mould for a clean release.

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To prevent the glass pulling in at the edges when it slumps into the top of the mould, make sure your glass is slightly wider (no more than 5mm) than the edge of the mould. This will stop the glass pulling in at the sides.

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If your breakers, or any similar tools, become stiff or begin to stick, make sure the mechanism is clear of debris and apply a small spray of WD40 lubricant. After a few minutes the tool should operate smoothly again. This should be done regularly as part of general maintenance of your tools.

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We generally fire a full fuse to 804C - full details of firing schedules are accessed from Kiln Schedules page in the Knowledge Base. Firing schedules for using Bullseye glass in our casting and slumping moulds can be found on the product page for each individual mould.

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Glass can change colour when it is used for casting, but it depends on the conditions inside the kiln and the shape of the object that you are casting.
Colours with Bullseye codes starting with 11-- or 14-- may appear black if used in certain thicknesses, as they are already extremely colour-saturated.
Transparent glasses that rely on cadmium, selenium or sulphur to create their colours are more sensitive to heat, and may turn opalescent if exposed to excessive heatwork.
The type of glass used also affects colour - a piece made with billet will have much better colour clarity compared with a piece made from frit, as when using a billet there is no space for air bubbles to form between glass particles. See Tipsheet 8: Basic Lost Wax Kilncasting for more information on selecting appropriate glasses for casting.

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A casting can be as large as the interior of your kiln will allow, but as a general rule of thumb the interior of the kiln should be twice the height of the final casting. Something important to bear in mind, especially for large castings, is that the piece must be heated and cooled uniformly to minimise the risk of suckers or thermal shock.

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Firing schedules for castings vary greatly depending on the mould type you're using, the process you're using and the glass you're using. Bullseye TipSheets are very helpful for casting advice. Find them in the 'Glass Techniques' section on our How To... Kilnforming Guide page.

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Firepolishing can happen anywhere from 593C to 804C, but the right temperature for different pieces depends on things like glass colour, rate of heating, and how much the surface has been coldworked. Firepolishing can also be achieved during slumping.

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There is no specific slumping temperature, as each glass project varies so much and has so many contributing factors. Generally, slumping temperatures are quite low and are held for a longer length of time than other processes in order to allow the glass to slowly sink into the mould. Bullseye have created many 'TipSheets' which offer very comprehensive advice for slumping all kinds of shapes - find the one you're looking for here.

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There are no specific temperatures for any kilnforming techniques, as different pieces will have completely different properties, and will therefore require completely different firing schedules. Please look at our Kilnforming Guides for basic information about each different technique.

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We generally fire a full fuse to 804C - full details of firing schedules are accessed from Kiln Schedules page in the Knowledge Base. Firing schedules for using Bullseye glass in our casting and slumping moulds can be found on the product page for each individual mould.

Jewellery and pendant moulds can make great pieces even using scrap glass. The main trouble people have is the glass spiking on the edges of the mould. The spikes are caused by the glass getting caught on the side of the mould as it melts. This can be solved either by using fine frit as the filler or piling the glass up like a pyramid in the centre so that it melts from the centre outwards.

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You do need to cool the glass rapidly to stop it dropping, this is done when you can see the glass has dropped to the point you were hoping.

Our Top Tips when using drop outs:

The blank should cover the outside diameter of the ring but not hang over the edge.

For drops under 10cm the optimum thickness of the blank is 6mm to 9mm.

For drops over 10cm the optimum thickness of the blank is 9mm to 12mm .

Fire the blank on a basic full fuse and anneal correctly for the thickness of the glass.

Use Bullseye separator on the dropout ring and also 1mm fibre, cut 3mm back from the ring edge.

The optimum top temperature is 650C to 700C depending on your kiln, glass thickness and how much you want to drop.

In plugin kilns remove the shelf for longer drops but remember to protect the base of the kiln with fibre paper.

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In a word, no. Not only is it really hard on the moulds and may cause them to shatter, but the thicker glass of a casting will not anneal properly. The casting could shatter in the kiln or worse yet, it could shatter for no apparent reason weeks later. We don't recommend using a microwave kiln for any glass fusing or casting work as the temperature cannot be controlled well enough to anneal the glass properly.

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We stock many different kilns suitable for glass fusing.  When choosing a kiln, consider the following:

Size:  If you are primarily focussed on jewellery making, or smaller pieces, then there’s no point in spending extra on a bigger kiln that will take up more room and cost more to fire. For jewellery makers, a small kiln like the Paragon SC2 would suffice unless planning to fire large numbers of pieces at once, and it also comes with an optional bead door. If you want to make large plates or bowls or bigger decorative pieces, then you need a kiln big enough to fit the work into.  Also consider the volume of work you wish to fire. If you want to fire more than a few pieces each day then you will need a chamber big enough to take the work. Remember that pieces will be in the kiln for the best part of a day. Lastly, consider the logistics. Will it fit where you want it to go? Can you get it through the door? If you are looking at a large 3 phase kiln, you will need to make sure you can get it wired into your power supply.

Controller:  Look for a controller that has pre-set firing schedules to get things started, but with the option of adding your own schedules.

Heating elements:  Glass requires even heat across its surface to fire correctly. Particularly with larger kilns, look for one with elements in the top, allowing for the heat to distribute evenly over the surface of the glass. If the kiln is deep to allow for three dimensional work, then it should ideally also have side elements to help the heat penetrate lower into the chamber.

Build quality:  We recommended only buying a kiln built by a quality manufacturer with an established history such as Kilncare, Skutt, Naberthem or Paragon (that’s why we stock them).  Prices of kilns vary, but generally the more you pay, the higher the build quality, the bigger the chamber and the more ‘extras’ you get like quartz elements or lid opening mechanisms. 

After sales service:  If you buy a kiln from us then we are on hand to talk you through getting started with your kiln, programming it and looking after it, for as long as you need it and at no extra cost. Everyone who buys a kiln from us also gets a 5% or 10% discount on products they buy from us in the future.

For more information, take a look at our YouTube video: Help Me Choose... Glass Kilns.

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A ceramics kiln can be programmed to fire glass, especially if you are doing glass casting but we would not generally recommend it. You may get issues like devitrification if you are fusing or slumping glass because ceramics kilns heat from the sides rather than the top, making the important even heating of glass difficult.  Also, ceramic work leaves pollutants in the kiln which can taint glass work causing problems such as devitrification or discolouration. If your only choice is to use a kiln which is also used for ceramics work, then we strongly recommend using a separate ‘glass only’ kiln shelf to try to reduce this problem.

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The bead door on the Paragon SC2 is so that after making beads using a flame you can anneal the beads in the kiln without opening the door every time. It is perfectly possible to anneal beads in a kiln without a bead door, but the specially designed door does make it easier to keep the heat in the kiln when you open it.

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We don't stock microwave kilns because we don't generally recommend using them to fuse glass. Glass needs to be heated and cooled evenly and in a controlled manner or it introduces stresses into the piece. In our experience,  microwave kilns heat glass the same way ordinary microwaves heat food: unevenly, which could make your work weak and more liable to break during or after firing.

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The bung is used to cover the vent hole in the kiln and the kiln can fire with or without the bung in place. Some firing schedules will recommend venting the kiln and if you want to vent the kiln you remove the bung, if you do not want to vent the kiln then the bung can be left in the hole.

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The cost of a firing depends on many factors, including the length of the firing, the firing temperature, how well insulated the kiln is, the power rating of the kiln and the cost of electricity. However an estimated cost of an average firing can be calculated as follows:

Power rating of kiln (kW) x time the kiln is firing for (in hours) x cost per kWh of electricity.

On an average full fuse our kilns are generally actually firing (using electricity) for approximately 3 hours. If the cost of electricity was 11.5p per kWh, and the power rating of the kiln was 2.5kW (e.g. Hobbyfuser), the cost of the firing can be calculated as follows:

2.5 x 3 x 11.5 = 86.25 pence

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We would not recommend using multiple shelves in a glass kiln. In the majority of glass kilns the heat is coming from above to promote even heating of the glass surface. If you stacked shelves the top of the kiln would be considerably hotter than the bottom resulting in a very uneven firing.

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