I have never tried adding black tin to cullet so I don't know. The yellow is the main color silver presents. If Calcedonia gets stirred, it turns gray. It is self defeating to gather calcedonia glasses. stirring is to be avoided. Heat treatment is really key to success. Hot then cold, then warm maybe then cool. Then hot, then cool. It goes on and on. I am currently making full pots of it at 80 lbs and there is no clear in the work at all but I do have three pots of the calcedonia, all tone different from the main pot. Fun but pricey. It looks like views from the Hubble.
Where are we going and why am I in this basket?