Topic: lead glass

[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]

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.

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.

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.

[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,

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.

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

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.

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?

[Frank]

Patent's at that time had more to do with Royal favour... who you know not what you know.

I would be more interested in the more recent research, just no time to track it down... any Glass Circle members?

[KevinH]

Makes me wonder what characteristics Ravenscroft's had that others lacked - why did he get so famous?

The list of Contemporary Records listed in Powell's book (see above) includes an entry:

1674. Petition of George Ravenscroft to the King for patent for seven years for his invention of manufacturing a sort of crystalline glass ... ... The Attorney-General ... reported that Ravenscorft's glass was made of ingredients other than those used in other glass-houses in England and the invention may be of considerable use as the glasses made thereby equalise if not excel those imported from Venice ... S.P. Dom.

Also, from The Art of Glass (Nerri / Merrett ) (2006 printing by The Society of Glass Technology), page 3 gives a general insight with:

... and a lead-containing glass suitable for making crystal vessels. This last-named development is usually ascribed to George Ravenscroft and the date of its realization as 1675.

Frank's point about patents in those days is important. They were not quite as we understand them now. And those granted to such as Clifford, Powlden, Tilston, and Ravenscroft were very likely for improvements on a generally known idea. Also, the meaning of "invention" as used in the 17th century was seemingly not as "tight" as many of us would prefer it to be these days!

The fact that Ravenscroft did get a seven year patent and certainly produced glass that successfully rivalled the Venetian products, at least in its stability, would seem to be the reason for his "fame".

But as mentioned before (some time ago) "glass of lead" is now known to have also been made in Holland and perhaps pre-dating Ravenscroft and the other English makers.

[krsilber]

None of that really answers my question about what characteristics Ravenscroft's had that the previous ones didn't.  Stability?  Workability?  Clarity?  Durability?  Ravenscroft went down in history for prefecting lead glass somehow, producing a metal that revolutionized the industry.  Obviously he was building on a long history of its use in glass, but it seems like if those before him had produced an good formula for blown crystal, it would have spread earlier. 

There are a couple articles about Ravenscroft in The Glass Circle 2 (avail. for 10 GBP here, incidentally) - is that why you asked about members, Frank?  Or different reason?  I'm not familiar with the organization.

[KevinH]

Sorry! I read the question as asking about a combination of "general characteristics together with the fame of Ravenscroft". I did not see it is a question of specifics of what the glass had that others did not, as I thought that point had been covered elsewhere and was known by most who had an interest in "glass of lead" ... the issue being that Ravenscroft's "difference" was mainly a progressive increase in red lead which gave rise to a more stable glass than had previously been obtained (as I tried to indicate with my comment, "... successfully rivalled the Venetian products, at least in its stability ...").

Amazingly, I had entirely forgotten about my first reading(s), a few years ago, of the articles about Ravenscroft in "The Glass Circle 2". Perhaps I just interpreted things as being "more technical" than in the general literature but not adding any new info in a general sense. I'll have to take another look at them soon.

[Frank]

The author is a member of the glass circle and members may have contact detaielos...

   See Peter Francis, The Development of Lead Glass, Apollo February 2000, pages 47 to 53


Ravenscroft is regarded as the inventor due to repetition in glass books that did not look deeper, just like Edison is commonly regarded as the inventor of the light bulb.