Combining Greens/Chromium-based with Cadmium-based Colors
We got a question recently about combining one of our greens - Sea Green - with other colors in deep encasements. The Sea green cracked in the line tubing prep. See photo below.
It is important to keep in mind the chemistry here and Momka shared some insights which we thought would be useful. The green colors we make are typically Chromium based. The yellow, reds and orange are typically Cadmium based. The different chemical compositions result in different cooling speeds and if you are working such a combo by hand, it is very tricky to keep the temperature even and also to cool the glass evenly if you are not encasing and combining everything in a crucible.
In addition, the Red/Yellow/Orange Cadmiums are softer - i.e., they have less density to them than the Chromium based greens. This also results is different tension and different levels of expansion.
If you are combining Cadmium and Chromium then, at a minimum encase the Chromium in a thin layer of clear glass. This will help with the cooling temp and the expansion somewhat. The layer can be thin so that it is not really disruptive to what you make. For best results encase all colors which you are trying to combine in such fashion and then combine them and melt and pull out of a crucible, vs just on your burner. It will be worth doing so if you are making multiple pieces or if you are producing a number of pieces from a big piece of prep.