Author Topic: Apsley Pellatt, the Falcon Glass Works, London  (Read 2691 times)

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Offline David E

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Re: Apsley Pellatt, the Falcon Glass Works, London
« Reply #10 on: February 04, 2010, 02:57:41 PM »
I've always wondered about cullet and the advantages of using it, but as glass that has been previously mixed, it should have good properties. But Ray Drury (former Chance chief engineer) was quite adamant that Chance's glass was far superior to Pilkington's because it used cullet. Strangely enough, Pilks in-house magazine, c.1960s, was called Cullet News!

So was this seen as a way to save money, or improve the quality of glass? I'll ask Ray. Of course, the differences between rolled-plate and fine lead crystal is poles apart!

But in a visit to the works at St Helens in 2007, it was evident that Pilks used cullet, with huge quantities of it being shoveled into the hopper, mixing with the sand and chemicals, prior to entering the tank furnace.
David
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Offline David W

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Re: Apsley Pellatt, the Falcon Glass Works, London
« Reply #11 on: February 04, 2010, 05:26:36 PM »
Glass Circle News has been running a series on the importance of cullet in founding glass. The forthcoming (March issue) includes an article by a recently retired professional expert on the subject. Its particular purpose is to reduce the melting time and temperature and so prolong the life of the pot/tank. All glasshouses generate a certain amount of cullet from their own furnaces which would have been available for making the best new glass. Cullet collected from other sources would probably have been used for a lower quality glass.
The article is about non lead glass and the author says a minimum of 10% is desirable.  For modern large scale melts it is crucial properly to clean it up first. It's worth a read (when it comes out next month) for those interested in the subject.


Offline David W

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Re: Apsley Pellatt, the Falcon Glass Works, London
« Reply #12 on: February 04, 2010, 05:57:25 PM »
Cullet -historical thoughts.

In my Glassmaking in London, p. 142, is reproduced a section of Rocque's 1746 map showing the Salt Petre Bank glasshouse near the Tower of London. Next to the glasshouse is shown what is clearly a huge pile of cullet labelled on the map as "Glass House Hill".

During WW2 I used to ride on my bike past the Glasshouse of Davey and Moore (Brimsdown, Enfield). I was always impressed by a colossal pile, some 8 or 9 feet high, of broken glass nearby sparkling in the sun. I was too young at the time to know why it was there but now I realise that it must have been cullet. There is more on this firm in www.glassmaking-in-london.co.uk.

When Pilks still had their own museum (some time in the 1970s?) I was shown round the float glass plant. The broken glass in large heap of batch being fed into the oven was clearly visible. When you see the glass coming out it makes you realise just how much batch has continuously to be fed in.

A glasshouse I visited in Damascus and another at Hebron, near Jerusalem, before the present troubles, both appeared to make their glass entirely of broken bottles in pretty crude oil-fired furnaces which is why I think it tends to come out with so many bubbles in it. Blue glass was made by stirring in a paste of copper salts (sulphate or nitrate I would guess.)


Offline David E

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Re: Apsley Pellatt, the Falcon Glass Works, London
« Reply #13 on: February 04, 2010, 10:30:10 PM »
Fascinating stuff - it's always with regret when we took things for granted in childhood, something which is now long gone :-\ Interesting that you were at Pilks when Ray was at Chance Bros, which meant regular trips for him up there. He was quite amazed when we were there in 2007, to see that Pilks was still using some of his installations on the rolled-plate plant. He left in 1976! I was also very impressed by how much was being fed into the furnace in the rolled-plate plant - a very impressive sight.

I see that map in your book is dated 1746 - quite amazing.

I got a speedy reply from Ray, which is most interesting:

Quote
We used a lot of cullet because it was much easier to melt and refine than frit.Pilks also used cullet but I don't know in what proportion. I used to know the proportion but not now but it must have been in excess of  80%, except when we were making coloured when a large proportion was frit to get the colour right. The cost was the main reason but cullet did improve the quality as the glass had already been refined. Quality control of the cullet was paramount. Ferrous was easily removed but a single aluminium bottle top could cost us a fortune in production.

I'll ask Ray to qualify the 80% figure - sounds like they were recycling more glass than they made!

Ivo might be able to expand on Middle-east glass production.
David
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Offline David W

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Re: Apsley Pellatt, the Falcon Glass Works, London
« Reply #14 on: February 04, 2010, 10:53:19 PM »

Yep! what Ray says fits exactly with my understanding of the situation.

However, I was thinking that increasing the proportion of cullet decreases the amount of frothing you would otherwise get from a raw batch. But Ray talks about adding frit which has already been cooked to remove the gases from the carbonates etc. Hence using cullet not only helps the melting it also saves on the preliminary cooking that would otherwise be required  for the batch.

I call that a win-win situation!!!

The article coming up in Glass Circle News talks about the rubbish that has to be removed from the recycle bin ranging from a banana skin to a handbag complete with contents.

Incidently, the batch for lead glass generates very little froth as most of the carbonate is replaced by lead oxide. So in that case the cullet could be added directly to the batch.



Offline David E

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Re: Apsley Pellatt, the Falcon Glass Works, London
« Reply #15 on: February 05, 2010, 09:02:27 AM »
Hard to appreciate molten glass actually frothing! :o But this could introduce tiny bubbles, which affects the clarity I suppose.

One glass technologist on this forum who has proved most helpful to us in the past is Adam Dodds (me in particular, my book, p.32), who might like to offer something about the industrialisation side of glassmaking. I'll give Adam a nudge.

Always fascinates me how the small addition of a chemical can drastically alter the mix and colour - although the story of throwing in the gold sovereign probably has some basis of truth, with a manager doing it to impress some clients, Ray's thought that a single aluminium bottle-top could have a really diverse effect is quite amazing, considering the massive bulk of glass in these tank furnaces.
David
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Offline David W

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Re: Apsley Pellatt, the Falcon Glass Works, London
« Reply #16 on: February 05, 2010, 02:01:03 PM »

Its not the molten glass that froths, it is the carbon dioxide released in the earlier stages of the melting process. In one studio glass experiment I saw described at an Association for the History of Glass meeting, quite spectacular pictures indicated that perhaps half the batch could be thrown out of the pot by frothing when the batch is added to an already hot pot. Fritting causes a controlled release of the carbon dioxide so that this does not happen.

As you suggest the residual bubbles do cause problems with fining which is why Bohemian crystal is often plagued with a myriad if tiny seed bubbles. This makes most early Bohemian crystal instantly recognisable. Masking this problem may be why much quality continental glass is so heavily engraved.

Full lead crystal glass does not suffer from this problem.


Offline Adam

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Re: Apsley Pellatt, the Falcon Glass Works, London
« Reply #17 on: February 05, 2010, 02:34:56 PM »
Thanks for the nudge, David E.  I would have missed this due to the well-known fact that very long threads do sometimes find the subject matter changing part way through.  One or two points I might make.

First, briefly a word of warning about the word "frit" when coupled with reference to Pilkingtons.  For some reason, Pilks used the word to mean the same as what all the rest of the industry called "batch", i.e. mixed raw materials which were not, so far as I know, "fritted" in the heat-processed sense used by most people.

David E., I think I can understand why people find the concept of glass "frothing" hard to visualise.  Remember we would be talking about glass at the temperature at which it is melted, which is a lot hotter than its working temperature which is how most people see it.  Think of warm or even hot golden syrup (and no, I haven't seen that froth!).  About five years ago, buried deep in a thread called "Glass Moulds" I said, following talk about stirring glass, I think, I said:-

"This sort of treatment was highly respectable and was (is?) used all over the world.  It was also called blocking, but we peasants always called it tatying.  It could be used for at least two different reasons.  The first was to use the large bubbles of steam produced to sweep away any fine bubbles (seed) remaining from the melting process.   The second reason, and the one for which I tatied most frequently, was to mix the melt thoroughly, usually if I was changing colours.  Anything which produces huge glugs of gas and generally stirs up the melt can be used.  The textbooks talked about wet banana stalks and the Germans reputedly used lump vitreous arsenic (arsenious oxide) which was very dense and therefore could be just chucked into the pot.  Big wads of wet newspaper have been talked about, but I'm not sure how that was used.  We used big potatoes, one at a time, cutting a hole in so that the sharpened end of the heavy rod (maybe 3/4" dia at least) could be forced in.   After maybe a minute of glugging, thumping and minor earthquakes the remains of the spud would break free and bob quickly to the top.  Molten glass does not wet carbon, so  the black thing was easily fished out.  Visitors were always surprised that the bit of spud left in the middle was still raw.  We would only need a second go if the spud came off the rod prematurely.  

  I vividly remember being called in once during the night because a pot of cadmium yellow (still a bit experimental) was refusing to clear of seed.  It must have somehow (I haven't a clue how) become  supersaturated with gas because when we tatyed it half the pot contents came out on to the floor looking like a cross between candy floss and something out of Quatermass!  That was the exception - tatying was normally a benign if spectacular process."

With hindsight, the excess gas might have had something to do with lack of cullet.  Any new composition obviously couldn't use cullet to start with because there wasn't any!  I cannot remember whether this was a first attept (zero cullet) or just early production (very little cullet).

Re cullet in general, I have made glass with cullet content varying from zero to 90% or higher.  At the extreme ends odd things might happen as described, but in general the amount used depended on what was available on the day.  I have little or no experience with bottle or flat glass production where "foreign" (i.e. not produced in-house) cullet is used and where tight economics may dictate a close watch on the effect of cullet ratio on melting rate.

Re sovereigns thrown in the pot I too have heard this one from trusted sources within the factories concerned.  I'm still not convinced and it was much too expensive to have a go myself!

Since typing the above, I have seen David W.'s posting, which also covers frothing.  Re fritting, David, was this actually done in the non-Pilkington sense of the word?

Adam D.


Offline David E

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Re: Apsley Pellatt, the Falcon Glass Works, London
« Reply #18 on: February 05, 2010, 06:31:22 PM »
Thanks for that Adam. I'll have to ask Ray Drury about his definition of frit. He was at Chance Bros. so there might have been some common usage of the term between the two.

I love the description of 'tatying'! ;D

David
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Offline David W

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Re: Apsley Pellatt, the Falcon Glass Works, London
« Reply #19 on: February 05, 2010, 10:51:45 PM »

Many thanks to  Adam for his comments although tatying is not quite what I am talking about.
To really answer this problem of foaming we need to get just a bit technical although I was always bottom of the class at physical chemistry. So I hope I have got the maths right!
Let us just consider the contribution of calcium carbonate the molecular mass of which in round figures is 100 g -1.

Now consider a batch with 10%  or 100 g of calcium carbonate in a batch weight of one kilogram.
By definition one gram  mole of calcium carbonate contains one gram mole of carbon dioxide which, also by definition,  would occupy, as a gas, 22.4 litres under standard conditions.

The combined gas law tells us that p1 x V1/T1  =  p2 x V2/T2 where p = pressure, V = volume and T = temperature under the initial (1) and final (2) conditions. However, p1 and p2 remain unchanged and so can be ignored.
The final carbon dioxide volume, V2, then becomes V1 x T2/T1
If we assume starting and final temperatures of 20 and 800 degrees C. This becomes 22.4 x 800/20 or that the gas has expanded 40 times. In terms of common units this is from about 5 gallons to about  200 gallons or, more realistically, about half that amount since the temperature rise is not instant. Even so, by any standards this is a big volume. And this comes from only 1000 grams of batch.
It is this massive release of gas during the early stages of founding that causes foaming and which the slower rise in temperature in fritting avoids. I think fritting normally stops at about 500 degrees C.

Adam’s tatying is not caused to any extent by this process but, as Adam correctly explains, by the water in the potato, wet paper etc. being turned to steam – albeit superheated steam. The potato itself only chars because to burn it requires oxygen and there in not much oxygen in a glass melt.

I take Adam’s point about Pilks frit. It raises the interesting question of how the gas volume change is managed in a float tank furnace. One solution would be to substitute calcium oxide for calcium carbonate. Or it might be controlled by the speed of batch addition at the cooler end of the tank which is a quite massive affair. Are their any of Pilk’s experts around to explain this?

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

 

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