Please Log In

Forgot your password?

Hop on board...

Are you a new Customer? Click here to register.


Preparing your kiln for firing: A look at primers.

Posted on 18th December 2013
Comments (0)

One of the first things you will need to do when you start firing your own work is choose a shelf primer. You can’t fire glass directly onto a kiln floor, shelf or mould as the glass will stick, so a thin barrier is needed. Here at Warm Glass UK we sell a number of different shelf and mould primers for this job, all of which have been tried and tested in our studio. I took a look at the pros and cons of each option:

Bullseye Shelf PrimerBullseye Shelf Primer

Our most popular kiln wash. Available in smaller quantities, a 400g jar will coat about 30 20” square shelves. It comes in powder form and you mix it with water before using. 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 706˚C, then you will not need to re-apply the primer for another firing. A new coating should be applied after a full fuse (766˚C or higher).  For more information on applying Bullseye Shelf Primer take a look at this information sheet:
Using Shelf Primer.

Hi Fire PrimerHi-Fire Shelf Primer

An excellent shelf primer, available in 5lb jars, 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 in Colour de Verre MouldPrimo 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.  Take a look at the video on this page for a demonstration of how to apply Primo Primer.

Boron Nitride SprayBoron Nitride Spray

Yes, 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 704˚C.

Thinfire PaperBullseye Thinfire Paper

Don’t want the hassle of preparing a primer and applying it? Try Thinfire Paper. 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.

Further information:

I found this great comparison guide from Devine Glass in Australia. I can only assume that the firing paper they trialled was not Bullseye Thinfire, as we have always found the Bullseye paper gives a nice smooth finish, but it is still very interesting reading:

This blog from the US site Glass Art by Margot compares Primo Primer and Bullseye Shelf Primer: Glass Art by Margot. Be careful if using a green scourer to clean your mould as she suggests. Use only lightly so you don’t lose detail in the mould.

One of our mould suppliers, the US company Slumpy’s, has a great blog. This one compares different mould primers and is worth a look: Slumpy's BlogSlumpy's logo


A Note about Shelves: Always use the smallest shelf you can when firing glass, and raise the shelf with props. This allows the heat to distribute evenly inside the kiln. Thin shelves are also preferable with glass work as thicker shelves absorb a lot more heat.

Safety Note:  Care must be taken to protect yourself from the dust when mixing, applying and removing all primers. Always wear a dust mask and gloves and read the safety information which comes with the primer.  We stock lots of safety equipment here.

Happy firing!

- Kirsty

Leave a Comment

Enable this picture
 Redraw Capture Image 
* This is to prevent unauthorised automated SPAM robots.