Wednesday, April 17, 2013

Walpole Wrath: Oster on Desag

Q: I was wondering if you might assist with a question: I am using Oster
Walpole on Desag clear, fired at 1050 ish, It's come up very wimpy, even
with 2 coatings. Should I try refiring w/o repainting hotter to get that
amber of my dreams? Don't want to screw up all the prior work...

A:Sorry to report your problem is not the stain or the temperature it's the glass itself. Desag's formula includes chemicals to make it more brilliant (less of an iron green) and subsequently the glass does not have the "receptors" for the stains. If you look at this chart from my tests on Oster stains you will see the reactions you can expect on various clear glasses. 
Oster stains go Amber on the tin side of float glass but if you want to get a deep amber on Desag you will need to switch to Reusche's Amber stain.
The last alternative to explore would be to try adding a small amount of sodium sulfate to the Oster stains. Unfortunately I can only point you in this direction as I have done no direct experimenting with Oster stain and sodium sulfate. It's mentioned in Albinas Elskus' book, The Art of Painting on Glass (pg 117) and I have tried it with Reusche stains. It will darken the stain but you will also get "metaling". You'll have to do your own battery of testing if you choose to go this route. If you are really trying to achieve the historic color that borders on deep orange - you're even more out of luck as it can only be achieved on a special glass known as "kelp or staining glass" which was produced in Britain in the 19th century. No one makes it today. However you can add your voice to my "petition" to Lambert's to research and recreate this formula for the benefit of us all.