Binders in glass: Color issues part II
In 2019 I was doing a lot of experiments with different binders and different colors of Bullseye glass. I was about to translate my notes into something useful when a surprise came out of my kiln that caused me to pause. I had been firing canary yellow as the best yellow with cellulose based binder. I had noticed that other opaque yellows I had tried took on a greenish tint. Then the unexpected happened. I ran out of the old jar of canary and switched to a new jar. I made my piece, dried it with a shape to it and fired it on wire mesh to hold that shape. It came out of the kiln a beautiful green. Ooops. I changed two things - was the green because it was a different batch of canary? I'd never know if the batches were different. Was it the metal atoms reacting from the wire mesh? I knew that Bullseye had offered new greens based on Fe (iron) at one point so maybe an iron reaction or a reaction to some other metal atoms in the SS mesh? I had planned to fire a new piece from the new Canary after cleaning my kiln thoroughly but life, the plague, supply issues and two dams breaking (months of really unreliable electricity) intervened.
Finally in 2021 I fired a new piece from the exact same batch mixed in 2019. I had a second piece I made at the same time with the exact same materials but never fired, so I ran it with out the mesh. Yellow was yellow.
Below you can see a sheet glass test tile on the right, canary used from two different jars in the middle that are color true and the strange case of green in the middle section of the piece on the far left. It's a nice green. Just sayin.
Conclusion: metal mesh in the kiln is probably a risky proposition with at least yellow and cellulose based binder. I have not re-run same batch same mesh or mesh and any other color or binder and I don't intend to. The mesh does oxidize during firing and I don't want the possible risk of stuff I can't clean adequately being a lingering problem.
Note that this was one firing at about 8 poise top temp to leave the top powder a little sugary. Sometimes that is striking. If not another low refire or tack will give me a finish I like.