27 - General Warnings for All the Colors
In order for colors to emerge in full beauty and perfection:
First, take note that every new crucible large or small, when heated for the first time leaves a residue of sediment in the glass. Any of the colours that are then made in them will be covered with grime and filth, but you can always glaze crucibles that are not too large with a coat of white glass, as is well known to the compositioners. By the second time the crucibles are used they will have lost that foul scum.
Second, take note, that these same crucibles large and small, should each serve a single colour. You must never add glass in order to make another colour. As an example, in any crucible than serves for yellow, you should never try to make garnet red, one that serves for garnet will make a very poor green for you, one that serves for red, will not make you a very good aquamarine, and so forth for all the colours. Therefore, every colour must have its own crucible, small or large, and in this manner, the colours will become closer to perfection.
Third, be sure that you calcine powders properly, that is neither too much nor too little, because in either of these cases they will not colour well.
Fourth, be sure to use the required proportions and doses, and make mixtures to correct proportion. The furnace should
be hot and stoked with hard dry
firewood, because the green and soft wood makes little heat and blows smoke over everything.
Fifth, be sure to divide the colorants. Use part in the frit and use part in the glass when it is fused and well clarified.
There are still other warnings that will be discussed in their
own places, when their particular colors are dealt with.