Designer, Artist, and Teacher, based in Far North Queensland, with a growing passion for Ceramics

Raku Glaze Test Tubes

In preparation for Form & Fire 2026, I tested some simple raku glazes (recipes below), and a couple of commercial low-fire clear/satin glazes, on a bunch of 'test tubes'. They were all numbered and have a line of texture, a diagonal stroke of wax resist, and one dip of glaze or two coats of brush glaze. I used two different groggy clays and used two different post-firing processes, one to get metallic shine or 'reduction radiance' via deep reduction, and the other to get 'cool crackle' via delayed/light reduction. (The alliteration helps me to distinguish between the two methods.) The sets of ceramic test tubes were connected together via heat resistant wire so that they could be placed into reduction simultaneously.

Tips for Reduction Radiance

Remove the pot from the kiln without delay and put it immediately into a metal container with shredded paper then put the lid on top. Use shredded newspaper instead of sawdust as it burns quicker than sawdust. Leave for 20-30 minutes. Generally, longer in the chamber equals more carbonisation (blackening) and deeper reduction.

Tips for Cool Crackle 

Remove the pot from the kiln and pause for a few seconds until you hear the glaze on the pot 'pinging', then put the pot into a metal container, cover with paper, allow to flame, then put a metal cover on top. Leave for about two minutes, lift the cover and allow the paper to re-ignite. Close the cover again and leave to reduce for about 15 minutes.

Simple Raku Glaze Recipes

9010 Clear Base
90% Frit 3124 + 10% Kaolin EPK = “the perfect glossy cone 04 glaze” according to Matt Katz on the For Flux Sake podcast Episode #19.

9010 White
The clear base as above plus about 10% zircopax (zirconium silicate)

9010 Copper*
The clear base as above plus about 3% red copper oxide

* I ran out of Frit 3124 so used Digital Fire's Raku Crackle Glaze Base recipe that I found on Glazy which uses 85% Frit 3110 and 15% Kaolin.

Turquoise Luster 

Beautiful copper in heavy reduction; lovely turquoise with crackle in light reduction. In Far North Queensland these materials are available via Cairns Potters Club (for members) or direct from ceramic supply shops like the Clay Shed. 

Frit 4110 = 100%
Copper carb = 3%
Tin Ox = 3%
Bentonite = 2%

I also added a couple teaspoons of Epsom salt solution as I found this glaze hard panned at the bottom of the bucket.