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lead glass

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Frank:
It was the use of white lead that was developed by Da Costa and co. It is interesting that this other lead compound was used to cloud glasss.

krsilber:

--- Quote from: Frank on July 18, 2008, 08:52:31 AM ---It was the use of white lead that was developed by Da Costa and co. It is interesting that this other lead compound was used to cloud glasss.

--- End quote ---

I didn't see where it specifically said lead antimonate was used for opacification, though it did say it was used in opaque glasses, but maybe I missed something.

I think it's important to keep in mind that the form of a glass ingredient before it's added and after it has become part of the batch are two different things.  The lead compound of the Da Costa white lead and the Egyptian lead antimonate may have been indistinguishable once in the metal.

The question of the development of the use of lead in glass seems to be highly complex.  Without the original documentation to refer to I start to wonder about way people have interpreted the data over the years.  For instance, was lead used by X for its effects on clarity or color, as a flux, or for some other reason?  Was it intentionally added, or was it an impurity in a mineral added for some other constituent?

Is it possible Ravenscroft was working on lead glass before DaCosta or someone else came along and shared his knowledge?

And now I find that something I thought so straightforward, the use of flint as a source of silica, is also being questioned.  The development of colorless lead crystal may be one of those topics that I'll leave to the historians.

krsilber:
I just found an interesting tidbit in a Google Book.  It's a quote from a paper read by Harry Powell at Whitefriars.  The Google page numbering is a little wacky.  The actual page I'm quoting from is 778 in the June 16, 1906 volume, Journal of the Society of the Arts.


--- Quote ---The credit of the discovery of lead-potash glass, which is now known as English flint glass, is given to Thomas Tilson, a merchant of London, who, "knowing the glory and beauty of glass of lead, found means to increase the charge of lead."  According to the Domestic State Papers of 1663, Tilson applied for and obtained a grant of the sole use and benefit of his invention of making crystal glass.
--- End quote ---

KevinH:
In H. J. Powell's book Glass-Making in England, published 1923, there are a few references to "Tilston (Tilson)" [pages 32, 34, 37, 122].

The first two are commenting on a point that,

--- Quote ---The total replacement of carbonate of lime by oxide of lead ... was not, as claimed by Mr.  Hartshorne, the result of a sudden invention by Plowden, or Tilston, or Ravenscroft, but of successive tentative experiments to make a more readily fusible glass.
--- End quote ---

The reference on page 37 covers an entry in a list of "Contemporary Records" and gives:

--- Quote ---1663. Warrent for a patent to Thomas Tilston, merchant of London, of sole making of crystal glass and looking glass plates, on surrender of a grant made to Martin Clifford and Th. Powlden the inventers. Patent to Thomas Tilston for fourteen years of the invention of making crystal and other glasses. S. P. Dom.
--- End quote ---

The page 122 reference is in regard to "Cast Plate-Glass" where comment is made on "the monopolies or patents" granted to Mansell, Buckingham and Tilston.

Harry Powell's book post-dates the 'paper read at Whitefriars' and the S.P. Dom. reference shows that the "grant for sole use" was for future use of a surrendered grant for use of a patent that already existed, not as a grant for an invention by Tilston (Tilson).

krsilber:
I noticed later last night as I was cruising Google Books that the paper was the basis for a chapter on cut glass in Powell's book.  I didn't read the whole chapter (I doubt it was all available), but saw that it was somewhat different; evidently he gathered more info about Tilston and lead glass in the meantime that I didn't see.  I just thought it interesting that there was apparently an English patent for lead glass that predated Ravenscroft's.  It's clear that there was a long history of use of lead in glass.  Makes me wonder what characteristics Ravenscroft's had that others lacked - why did he get so famous?

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