I didn’t leave empty handed. In one of the last envelopes I found a file folder marked “Complete Red Formula”. It was about 18 pages long! What I now know is that it is not a matter of simply having the recipe but you must also know how the glass was worked by the gaffer.
Saint’s formula required a furnace with 4 crucibles. Two of them held a mixture of “green white” – basically a clear glass with a green cast. Another contained a glass to which yellow “flowers of Sulfur” had been added and the final was a red made by the addition of “Copper scales”. The procedure was to melt these, then take the yellow, ladle it into the red and stir it 100 times. The glass blower would form his bubble from a series of small gathers, first in the clear, then in the red in a succession of 5 dips ending in clear. Stirring would ensure that the layers of red were streaky and casing with clear would prevent the color from being too dark.