By all means, use my description. I'm glad it was understandable since its very difficult to describe a process you are familiar with to someone who isn't. You always leave something out. I'll add that chalk was well understood as a polishing agent for metal in at least the early 18th century and very likely earlier. For instance, the locks and barrels of military firearms were customarily very highly polished. In the field soldiers would use powdered brick dust on a wet rag but chalk is frequently described as the polishing agent actually used in manufacturing.
I suspect that the drawback to using male/female laps against each other is that both pieces will wear. I am guessing that if the lens maker had a set of gages like I used, which are simply used to check the curve, the lap could be spun in any lathe-like machine and the surface selectively filed or ground to return it to true. As I've said, I held the lap and the gage up to a window and looked for a streak of light between them...a very accurate way of measuring once you have some practice and know what to look for.

One criticism of the reproduced tool illustrated here. I also suspect that the lenses were either convex on both sides or, more likely, flat on one side and convex on the other (like modern rifle scopes. This would make it much easier to find the optical center of the lens and trim the outer edges accordingly.) One of my jobs was called "layout" where, using a prescription as a guide, I would mark the desired optical center of the lens with a little sharpened stick dipped in india ink. You'd think this was practically impossible but after a week or so of doing it you can literally get it within a fraction of a millimeter. The little metal piece I described was positioned so that the center hole was directly over the optical center. Again, its sounds almost impossible but with practice you come very close with very little effort.

The power of the lens represents the total of the inside and outside curves so I suspect that the "grinding cup" (for lack of a better term) on this reproduction has much too deep a curve. Its the sort of subtle difference that a period artist might easily fail to understand. It would actually be quite easy to replicate the process I used for experimental purposes and I think you'll find that much less curve is in order. I once made a pair of sunglasses out of the bottoms of Coke bottles...terrible glass, soft and full of bubbles but it could actually be done!

I also have the 1723 French edition of Isaac Newton's "Traite du Optique" which I suspect contains much pertinent information from only 100 years after Spinoza. the text may well contain information on how things were done and when advances took place. Unfortunately I can't read French but there are numerous copper plate engraved illustrations. Let me know if you'd like me to try to photograph some of them for you.

I haven't thought about this stuff in more than 30 years buts its really odd how it comes back.

Another memory just came back...I think that the felt was attached to the lap with fish or hide glue. The lens was checked by holding it up to a light bulb with a single filiment. You held it in such a way that the light from the filiment reflected off the surface. If there were no breaks or nicks in the reflection, the lens was perfectly true. This could also be done by stretching a hair across a window and picking up the shadow. You could never see the imperfections with the naked eye. Now I'm beginning to feel like a "living history" exhibit!

(my 3rd edit) Will this ever stop? The lens was finished in what we called an "edger" which was nothing more than a lathe-like spindle that gripped the little metal piece glued to the lens and spun it against a grinding wheel. These were not the modern clay-based wheels but slow turning natural stone wheels that ran in water, the grinding wheel turning one way and the lens in the opposite direction. In this way the outer edge was gradually reduced in a manner perfectly concentric with the optical center. Even if the metal attachment was slightly off center on the original lump of glass, this process insured that it would be perfectly concentric when finished. You could only remove the metal piece after this was done and you could not replace it perfectly so it was a once-chance-only affair.

Joe Puleo