Many thanks for your explanation. I am sure it is not the first time that practice has not behaved according to theory. I was moved to look up another glassmaker , Harry J. Powell, Glassmaking in England. He, page 13, quotes another ancient , Theophilus (c. 1140), as follows:-
“A mixture of the extracted alkali with sand and a small proportion of lime was heated in the calcar (a type of reverberatory furnace) until partly fused. When cool the fused mass, called “frit”, was broken into fragments and shovelled into crucibles standing in the melting furnace. In the crucibles the frit melted, became fluid and threw to the surface a scum of impurities. After the scum had been removed by skimming the remaining glass was ladled into pans of water. The water was drained off and the glass, when dry, was replaced in the crucible for final melting.”
Unfortunately, according to this translation, Theophilus does not explain the workings of the fritting process although it becomes clear that the batch ingredients leave much to be desired. I don’t suppose that you were troubled with scum, ladling into water etc.
It is always dangerous to try looking up the original text and when I turn to the translation of Theophilus by Hawthorne & Smith (Dover Books, 1979) I read :-
Chapter 4. The Mixture of Ashes and Sand.
“When you have arranged all this (i.e. built the furnace), take beechwood logs completely dried out in smoke, and light large fires in both sides of the bigger furnace. Then take two parts of the ashes of which we have spoken before, and a third part of sand collected out of water, and carefully cleaned of earth and stones. Mix them in a clean place, and when they have been long and well mixed together lift them up with the long handled iron ladle and put them on the upper hearth in the smaller section of the furnace so that they may be fritted. When they begin to get hot, stir at once with the same ladle to prevent them from melting from the heat of the fire and agglomerating. Continue doing this for a night and a day.”
That’s it. There is no account of what to do next as the Powell version suggests. And there is no mention of frothing.
How one equates these two quite different accounts is a problem. It has been suggested that Theophilus got his account from an even earlier one by Binguccio. Perhaps Powell was quoting the wrong author!
What is annoying though, is that although Powell explains all this historical stuff he does not say what they actually did at the Whitefriars works.
There is no need to reply that you did none of the above.