Topic: Apsley Pellatt, the Falcon Glass Works, London

[David E]

Re sovereigns: I understand that these were thrown in the pot but that they definitely did not colour the glass ruby.

Just a quickie to say that I always thought this story was linked to Bristol Blue?

[David W]

In my post  (#9 Feb. 3rd) on the source of glass sand used by the Pellatt works I gave the date of Apsley's book as 1859. It should, of course, have been 1849 so that there was a twelve year gap between it and the 1861 Busy Hives Around Us article.

By 1861 Apsley had long been involved in parliamentary affairs and his younger brother, Frederick had been running the factory for some nine years.  This time gap may explain the different sources of sand stated to have been used by the two authors. The different sands said to have been used shows that the Busy Hives article was not just a rehash of Ashley's book.

As with any historical detective work the time scale of the sources of information must always be considered. One frame does not always give the complete picture.

My apologies for the date error.


PS. Sorry David E, I do not understand how Bristol Blue (glass coloured by cobalt in the form of smalt) has any connection with gold ruby.

[David E]

PS. Sorry David E, I do not understand how Bristol Blue (glass coloured by cobalt in the form of smalt) has any connection with gold ruby.

Not a problem: I would never purport to be a technologist, but it was just that I remembered a topic on this forum some time ago where I thought it was stated that gold chloride was used in true Bristol Blue (not the modern cobalt variant), hence the gold sovereign fable, but perhaps I got it wrong

[KevinH]

For clarification (or not?) David's reference to gold chloride and 'true Bristol blue' appears in two earlier topics in the Board:

Identifying Blue glass..........Bristol, Cobalt, Irish?
What's "Bristol glass"?

[David E]

Thanks, but I may have been listening to my own rumours! 

[Adam]

David W. - While accepting your sums (without checking them myself - I trust you!!) I don't quite understand the point about frothing (forget tatying).  In normal melting, pot or tank, using sodium and calcium carbonates in the normal way, I have never had any frothing problem nor have I heard of it happening to anyone else.  Of course frothing occurs, but not sufficiently to be a nuisance.  Having said that, we always filled our pots twice, the second time after the first fill had died down.  I suppose if we had stuffed as much batch as possible into an empty pot we might have had a problem, but why do that?  Am I missing a point somewhere, not having read every word of the thread?

Adam D.

[David W]

Adam:-Your points are well made.      So the question is why, accepting the evolution of a large amount of CO2 and that the traditional way of overcoming this problem was a preliminary fritting (it is documented as the way used in 16th century Venetian glassmaking, for example*), do you not find it necessary?

The maths point up the huge gas expansion associated with temperature rise and my guess (no better than that) is a combination of modern furnace control and the speed of addition of the batch to a (relatively small?) pot. I guessed that Pilks use of raw batch in their float line might be controlled in this way.

I have never seen a pot being charged but I have watched a parison being rolled over a thin layer of sodium bicarb.in order to fill it full of decorative bubbles. So the effect is there, it must be a question of control.

 I wonder about the temperature of your pot at the time of charging and what you mean by "allowing it to settle"� before the second addition and for how long? At a conference in Dublin some while ago we were taken to see some studio glass blowing but it turned out that the pot had only been charged for an hour or two and the glass, although fluid, was still too viscous to work. How long does it take for a batch to get to the point of use in a modern furnace?

Pellatt describes the length of time it took to found a pot of glass and how even this depended on whether or not the wind was in the right direction. The tradition of the glassworkers living on site and a bell being rung when the "crisis" (as it was called) was reached and the glass ready to work, were all part of this problem.

From what you say it does seem to me that modern technology has made it possible to eliminate the fritting process, an improvement I have not seen described before. What do you think?

*Moretti, C. And Toninato T, (2001) Ricette vetrarie del Rescinamento (Glass recipies of the Renaissance), Marsillo pub. The fritted product was described as "breads"� (i.e. lumps the size of a bread roll and was stored as such for future use.) The Venetian texts never mention the use of cullet and I wonder how the batch to cullet ratio would also affect this problem.

[David W]

Adam, I owe you an apology.
I have just quoted you as writing "allowing it to settle" when you actually wrote "allowing it to die down".
I have not yet discovered how to see your text and write a reply at the same time. Can anyone help on that?
So although I hope my quote means the same my apologies again for getting it wrong.

[David E]

how to see your text and write a reply at the same time

Just scroll down - the full textual content is there when you reply to a topic.

[Adam]

Both Davids - Many thanks for asking and answering the question about seeing what one is replying to.  After all these years I hadn't noticed that I can scroll down just like answering an email!!.

David W. - You have mentioned 16th century glassmaking.  Now my glass technology is years out of date by most standards (I quit the industry 38 years ago and didn't have much to do with the melting side for ten years before that) but relative to the 16th century I must be fairly modern!!  If, as you suggest, fritting was used back then (and I wouldn't know) then "modern" practice has certainly eliminated any need for it.  Copious amounts of carbon dioxide, water vapour and (sometimes) nitrogen oxides are given off and for the last hundred years at the very least (and even I can't go back much further!) they have not represented the slightest problem. 

Batch when heated starts to bubble up as the components start to decompose and, if filled on top of existing glass (always in a tank furnace: usually in a pot) it will remain floating on top.  I suppose you could call it frothing, but that is a dangerous word in this thread!  Eventually it will settle down to something like glass but full of bubbles.

Re pots, David, ours held about a ton.  In our 12-pot furnace we would work six pots every other day, so the total time between first filling and working would be under 40 hours, but in many cases the time could be cut if it fit the shift working.  The second would usualy be five or six hours after the first, in some cases followed by a third at the furnaceman's discretion.  Nothing to do with frothing - simply the wish to achieve a brim full pot of good glass.  Present-day single pot furnaces could be much quicker than that depending on available temperature, open or closed pots etc. etc.

Re continuous tanks, the principles are much the same whether small 10 ton ones like ours or 1000 ton plus jobs as used in the bottle and flat glass industries.  In all cases the batch is fed in one end at a rate compatible with how much is being pulled out the other end.  In all cases some means is provided (often a solid barrier with a submerged hole or "throat") to hold back floating, partially melted batch in the "melting end" and to allow a drop in temperature in the "working end".

Small studio glassmaking has mushroomed enormously since "my" time.  The small quantities involved must mean that in many cases they would prefer to buy in batch from outside.  I know nothing about this (Adam A.?) but at the risk of opening another can of worms I would not be surprised if some form of fritting took place simply to make handling less dusty.

Adam D.