Andy,

Percy p.144 refers to Baker's experiments on removing copper and other 
impurities from lead by crystallisation.  He was obviously doing this on a 
lab scale and performance at full scale can often be better.  I saw it being 
done at  (I think) the Berzelius works in Duisburg where lead from an 
Imperial Smelting furnace was held at about 450 deg C for 3 days with 
extremely gentle stirring.  The coppery dross came to the surface as a fine 
dust.  Perhaps other contributors to the discussion group have better 
details.  We were told that no additions were made and separation relied on 
the mutual insolubility of copper and lead.   At the time it surprised me 
because I thought decoppering with sulphur had become universal practice.

Decoppering with zinc (Percy p.174-6) seems to have been not much more than 
an experiment with perhaps some development to full scale in Germany.  Of 
course, it's the basis of the Parkes Process for removing silver and Baker's 
results show this very well.

Percy (p.517) refers to the use of slag lead as part of the charge in red 
lead production and says that this was done because small amounts of 
antimony in the slag lead gave a brighter glass.  Copper was said to 
accelerate the oxidation to red lead and much of it remained behind in the 
un-oxidised lead.

There are several mentions (Yorkshire, N. Pennines)  that some lead fume 
from condensers and the upper parts of long flues was not resmelted but sold 
directly to manufacturers of white lead pigment (basic carbonate) and was 
much sought after.  This could be identified because it was white whereas 
flue dust from the lower flues would be grey or black and would contain 
unchanged concentrate and soot.  White fume would have been the result of 
condensed volatilised lead and impurities such as copper and iron would be 
absent or much diminished.  These elements would affect the colour of the 
white lead.  Impurities such as antimony and zinc which might have been 
volatilised would have been tolerated as they did not impart colours to the 
pigment.

Snailbeach lead seems to have been mentioned by Percy and probably because 
he spoke to nearby glassmakers in the Black Country - other makes of lead 
would have probably worked.  Elsewhere he states that W.B. lead from the N. 
Pennines was recommended for making white lead.  Certainly this was a 
reputable brand and produced in such quantities that it was widely 
obtainable.  W.B. lead would have come from many different mines and 
smelting mills and this clearly demonstrates the commercial advantage in 
marketing under a single brand name.

Best wishes to the Group for a merry festive season and a successful New 
Year.

Richard.

-----Original Message----- 
From: Andy Cuckson
Sent: Sunday, December 24, 2017 9:26 AM
To: [log in to unmask]
Subject: Re: Copper pyrites in lead - removal of, for glassmakers' red lead

Richard, many thanks for your informative reply.


I would guess this is the same W Baker who wrote ‘On the Impurities 
contained in Lead and theirInfluence on its Technical Uses’ in Mining& 
Smelting Magazine Vol.4 (1863) pp.201-204,  which pushed me to ask the 
question. In this, he does not admit to having done any experiments to 
remove copper himself, and gives no dates.

I have now found Percy's 'Metallurgy of Lead' (1870) on the internet, and if 
you mean the description pp.174-176 'Decopperization of lead by zinc', this 
seems rather an expensive process. Regarding users specifying a particular 
brand for the job being a tradition - it would seem to have been a sensible 
policy in this case. Why spend all that time and money when you know you can 
buy Snailbeach lead with less than 1% copper to make your red lead for the 
flint glass trade? In Percy, the first large scale experiment in lead 
decopperization was stated to have been done in 1861, while the West 
Midlands glessmakers' red lead producers were still buying Snailbeach lead 
decades later.

J & H Lloyd of Handsworth, who supplied glassmakers' red lead, bought 
Snailbeach slag lead specially, and this might have been in addition to pig 
lead. When J & H Lloyd was bought by Best & Lloyd in the 1880s, they then 
bought Snailbeach flue dust lead. Adkins of Handsworth, a rival, said in 
1882 that nothing other than the flue dust lead would do for their work. 
Snailbeach slag lead and flue dust lead were produced using a Castilian 
furnace.

Any ideas what advantages these raw materials might have over the general 
lead?


Any further contributions welcome - Season's Greetings to one and all.

Andy Cuckson







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