Topic: Flint Glass. What is it?

[Anne]

Moved back from Archive for further discussion

[Ivo]

Thanks for that, Anne. The matter has been discussed quite extensively above, but confusion still remains. Flint is 1/ a technical term for early lead glass and 2/ used as a term for clear glass by some glassmakers. Different things to different people - I think that is where the confusion starts. @1 we have sodalime, semicrystal, lead crystal and superior crystal @2 we have the term "clear".

[krsilber]

Yes, thanks, Anne.

First I want to address the main reason I wanted to bring this thread up again.  In Frank's summation he says,

"Flint was used as a source af silica dioxide and used as an alkali for glassmaking. (It is likely to be shown in more modern recipes as SiO2 or Silicon Dioxide or just Quartz).

It appears to have been largely displaced by Lead Oxide and other alkalis."

I don't think this is totally correct.  Flint was used for silica, correct, but it was replaced by sand.  Neither flint nor lead is an alkali, and flint had nothing to do with the use of lead except for the fact that Ravenscroft's first lead glass incidentally used flint as the source of silica.


Now a few questions for Ivo - why would flint be technical term for early lead glass when the earliest true flint glass was lead-free?  It doesn't strike me as a technical term at all (though I guess it depends on one's definition of "technical term"!).  I agree wholeheartedly it means different things to different people.

Is the "sodalime...superior crystal" a progression of more and more lead added to the batch?  What is superior crystal?

Is "clear" the common name for colorless glass in the UK?  That's worse than our use of the word "crystal" for it!

[Frank]

Soda-ash, flint is definitely NOT a PbO glass.

Seeminly not neccesarily:

Continuing alternate points of reference from a French source 1894, analysis by M. Dumas

			Flint
	Cristal	vs.	Glass
Silice	56,00		42,50
Potase	8,90		11,70
Chaux	2,60		0,50
Alumine	-		1,80
Oxyde de plomb	32,50		43,50

The table includes four types of non-lead glass: Verre à bouteilles, Verre à vitres, Verre à glaces, Verre à gobleterie.

[krsilber]

Since last reading this thread I've come across multiple texts that treat "flint" ambiguously in terms of whether it has lead.  Just a couple days ago:
"Under the caption of flint, or crystal glass, many varieties of glass may be properly classed...Such titles as 'lead flint,' 'lime flint,' 'tank flint,' 'German flint,' etc. are applied to glasses graded according to materials used and circumstances contingent to their manufacture."
(Elements of Glass and Glass Making, Benjamin Biser, 1899)

(The same book has a brief discussion of..."Guano seems to be the only substance which will impart a white opacity to glass, and yet be economical in cost and effect on pots.")

[Frank]

BirdsInit makes white glass, yes I kno-ow  we have skylights  :spls:, it's the cleaning costs!

booo beat the s**t censor on a quick edit 

[Frank]

Final confirmation of Ivo that it was originally lead glass, sort of poetic to discover it was first developed in Holland:

http://www.glassmessages.com/index.php/topic,10321.msg124233.html#msg124233

[krsilber]

Hmmm, I'd like to read that and see what his references are.  Why does everyone else believe that Ravenscroft developed it "working in London in great secrecy" (Short History of Glass, Zerwick)?

The idea that the lead was derived from flint...well, I'm no geologist, but that seems a little fishy.  Flint is silica with not a lot of impurities, which is why it was used.  And it's HARD, and not that heavy.  Was the lead extracted from it beforehand, and if not, how could the amount of lead be controlled?

[Ivo]

Final confirmation of Ivo that it was originally lead glass, sort of poetic to discover it was first developed in Holland:

hey leave me out of this I have nothing to do with it, it is WAY beyond my cutoff dates.

[Frank]

Flint is 1/ a technical term for early lead glass and 2/ used as a term for clear glass by some glassmakers.