Hunh. This is weird.

[xiphias]

According to the particular Daf Yomi bit on LJ I read:

In connection with the preceding discussion of the laws of purity, the Talmud mentions the purity of glassware. Since glassware is not mentioned anywhere in the Torah, it should not be susceptible to ritual impurity. However, the Sages did decree such impurity. Why? Rabbi Yochanan quoted his favorite student Resh Lakish: "Since its formation is from sand, the Sages placed it in the same category as earthenware – which is mentioned in the Torah and is susceptible to impurity, though only from the inside."

This is supposedly somewhere in Shabbat 16, and I'm trying to find it, because it strikes me as weird. This suggests that the Sages knew about how glass was made, and, if so, it suggests that educated Jews throughout history ought to have know how glass was made, or, at least, to have had a really good clue, from reading that passage.

But, for centuries in the Middle Ages, Venice managed to maintain a monopoly on the secret of making glass -- a secret that there would have been a lot of money to be made in breaking. So how was it that that piece of information wasn't used to figure out that trade secret?

Comments

[temima.livejournal.com]

What else is involved in making glass? Where and when was the passage written? Not rhetorical questions, I do want to know.

[papersky.livejournal.com]

The secret was blowing glass. Anyone could make lumpy earthenware style glass -- faience and so on. They knew how to melt sand and slosh that about. They knew glass was made out of sand, they didn't know how to colour it and blow it into thin delicate Murano glass -- it was the techniques and the dyes that were the secret, not the sand.

[sinboy.livejournal.com]

Exactly

[cellio]

It's actually at the bottom of 15b (continuing onto 16, but the part about R. Yochanan is on 15).

Didn't the Romans have glass? Not nice thin even glass like we think of, but glass nonetheless? This is the first I've heard of it being used then for dishes, though.

[browngirl.livejournal.com]

The Romans had glass, and I think even developed a transparent blue-green tinted variety. I don't think it was used how we use i nowadays, though -- more for jewelry and small bottles and so on.

*makes a note to look through my books sometime and find out more info on the subject*

[dhole.livejournal.com]

Reish Lakish lived in the third century, IIRC. Assuming that linking to a search result will work here, http://www.metmuseum.org/collections/search-the-collections?pg=1&what=Glass&when=A.D.+1-500&ft=*&noqs=true should give you a sense of what sort of glass people around then were using. Otherwise, a google image search for 3rd century glass will get at least a few relevant pictures.

[shmuelisms.livejournal.com]

As has been said, the secret was in the specific details. But also you presume that 1) knowledge doesn't get lost 2) that those *fluent* in the Talmud would have a strong business interest 3) that Jews were in a political/social position to upset strong [Christian] monopolies. No small number of Christian clergy ALSO studied the Talmud at the time.

[tober.livejournal.com]

Knowing that glass comes from sand doesn't even require the ability to make glass (although making glass only really requires sand and a sufficiently hot fire, anybody who had developed something like a forge or kiln could, at least in theory, make little glass baubles). It only requires the observation that sand + lightning = a fulgurite and that a fulgurite = glass (albeit very crude glass). I don't actually know, but my suspicion is that any society that had a word for glass and made a clear distinction between glass and earthenware understood that glass was made from sand.

Also, not completely related - it seems to me possible that some of the ancient glassmakers of Venice were Jews.

[cakmpls.livejournal.com]

We all have odd gaps in our knowledge (certainly I do!), and I mean no disrespect to you, but the idea that Venice was the only place glass was made in the Middle Ages, not to mention preceding centuries--indeed, millennia--is one of the oddest I have run across.