# Ancient methods: Salt Cementation.



## HAuCl4 (Aug 6, 2010)

Found this in wikipedia and other web search. Maybe just general interest or maybe a trigger for ideas. Enjoy!.  

Theophilus was a 12th century German monk and in his book ‘’De Diversus Artibus’’[12] gives the clearest description of the salt cementation process.

“ break into tiny pieces a tile or piece of burnt and reddened furnace-clay and when it is powdered, divide it into two equal parts by weight and add to it a third part of salt of the same weight. It should then be likely sprinkled with urine and mixed so that it does not stick together but is just moistened. ” 
—Theophilus[13]


This mixture is then added to an earthenware pot and layered with thin sheets of gold fold. The pot is then sealed and heated in a furnace.

“ Then put the fire and wood below and see that a plentiful fire is not lacking for the space of a day and a night. In the morning, however, take out the gold and melt it again, hammer it, and put it into the furnace as before. After another day and night take it out again, mix a little red copper with it, melt as before, and put it back into the furnace. And when you have taken it out a third time, wash it and carefully dry it. Weigh it, when dried, and see how much has been lost, then fold it up and keep it. ” 
—Theophilus[14

The Method of cementing gold and of Bringing it to its Ultimate Fineness-Vannoccio Biringuccio

http://books.google.it/books?id=ruBbKRKGeOwC&pg=PA202&lpg=PA202&dq=The+Method+of+cementing+gold+and+of+Bringing+it+to+its+Ultimate+Fineness&source=bl&ots=hiijeUwTzS&sig=tp9DXpELlCoqPTUMy955BxI33S0&hl=it&ei=jwxcTMnCJ4P_8AaElfDuAg&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBUQ6AEwAA#v=onepage&q=The%20Method%20of%20cementing%20gold%20and%20of%20Bringing%20it%20to%20its%20Ultimate%20Fineness&f=false

Modern re-creation of salt cementation methods by Notton:

Salt cementation
This process was used from Lydian to post medieval times. It is a solid state process relying on common salt as the active ingredient but it is possible to use a mixture of saltpetre (KNO3) and green vitriol (FeSO4). The basic process involved the mixing of argentiferous gold foil (in later periods granules were used), common salt and brick dust or burnt clay in a closed and sealed container. Theophilus mentions the addition of urine to the mix. With heating, the silver reacts with the salt to form silver chloride which is removed leaving a purified gold behind. Conditions needed for this process are below 1000°C as the gold should not melt. Silver can be recovered by smelting the debris.[18] Heating can take 24 hours. Hoover and Hoover[19] explains the process thus; under heating salt (sodium chloride, NaCl) decomposes in the presence of silica and alumina (from the brick dust or clay) to produce hydrochloric acid and also some chlorine. This reacts with the silver to produce silver chloride (AgCl). The urine is acidic and aids decomposition. Silver chloride is volatile and would be removed from the metal. And the container is sealed to stop the escape of the silver which can be recovered later. Notton in experiments found that with one heating the gold content could be taken from 37.5% to 93%[20]


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## qst42know (Aug 6, 2010)

The clay or brick dust may may act as a cupel does absorbing base metal oxides. Urine is a primitive source of nitrate. And salt is a highly fluid flux recommended in early texts on fire assaying. 

That's an interesting little alchemist like snippet. 8)


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## Chumbawamba (Aug 10, 2010)

I always wonder how ancient peoples figured out the stuff they knew. In this case, I can only imagine that someone was trying to put out a fire while trying to refine gold one day and all he had was his piss. After finding a much purer gold ingot than he expected and with some careful primitive deduction he realized what he had done and through experimentation perfected the process.

That's my theory, anyway


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## HAuCl4 (Aug 10, 2010)

I'm also amazed at what they could achieve, with very little if any available resources and technologies.


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## philddreamer (Aug 18, 2010)

Chumbawamba wrote:
I always wonder how ancient peoples figured out the stuff they knew. In this case, I can only imagine that someone was trying to put out a fire while trying to refine gold one day and all he had was his piss. After finding a much purer gold ingot than he expected and with some careful primitive deduction he realized what he had done and through experimentation perfected the process.


Hummmmm... Very interesting theory! 
Or maybe an ancient civilization of MacGyvers. :roll:

Very interesting post HAuCI4.

Phil


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## g_axelsson (Aug 18, 2010)

Chumbawamba said:


> I always wonder how ancient peoples figured out the stuff they knew. In this case, I can only imagine that someone was trying to put out a fire while trying to refine gold one day and all he had was his piss. After finding a much purer gold ingot than he expected and with some careful primitive deduction he realized what he had done and through experimentation perfected the process.
> 
> That's my theory, anyway



Actually, the alchemical theories were based on what you could perceive of certain substances. As urine is golden in color it was a quite common component in alchemy. The discovery of phosphorus was made by a German alchemist trying to create the philosopher's stone by boiling down urine....
http://en.wikipedia.org/wiki/Phosphorus#History_and_discovery
... makes me wonder if that is why phosphorous have the chemical notation *P*...

:mrgreen: 

/Göran


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## glorycloud (Aug 18, 2010)

LOL! good one!


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## HAuCl4 (Nov 24, 2010)

http://en.wikipedia.org/wiki/Refining_(metallurgy)

Cupellation
One ancient process for extracting the silver from lead was cupellation. Lead was melted in a bone ash 'test' or 'cupel' and air blown across the surface. This oxidised the lead to litharge, leaving a button of silver. In ancient times, the litharge was discarded, but more usually it was re-smelted to lead. "Pigs" of Roman lead have been found marked EX ARG (argentum is Latin for Silver). This presumably indicated that the lead had already been de-silvered. This process was viable[when?] economically if the lead contained[clarification needed] 8 troy ounces of silver per ton of lead (178 ppm).[citation needed]

In the 18th century, the process was carried on using a kind of reverberatory furnace, but differing from the usual kind in that air was blown over the surface of the molten lead from bellows or (in the 19th century) blowing cylinders.

[edit] Pattinson process
The Pattinson process was introduced in 1833. It depended on well-known material properties; essentially that lead and silver melt at different temperatures.[citation needed]

The equipment consisted of a row of about 8-9 iron pots, which could be heated from below. Lead was charged to the central pot and melted. This was then allowed to cool, as the lead solidified, it was skimmed off and moved to the next pot in one direction, and the remaining metal was then transferred to the next pot in the opposite direction. The process was repeated in the pots successively, and resulted in lead accumulating in the pot at one end and silver in that at the other. The process was viable down to 2-3 troy ounces[clarification needed] per ton (45-67 ppm).[citation needed]

[edit] Parkes process
The Parkes process, patented in 1850 uses zinc to form a material which the silver enters. This floats on the lead and can be skimmed off, enabling the silver to be recovered.

[edit] Copper
[edit] Fire refining
The initial product of copper smelting was impure black copper, which was then repeatedly melted to purify it, alternately oxidizing and reducing it. In one of the melting stages, lead was added. Gold and silver preferentially dissolved in this, thus providing a means of recovering these precious metals. To produce purer copper suitable for making copper plates or hollow-ware, further melting processes were undertaken, using charcoal as fuel. The repeated application of such fire-refining processes was capable of producing copper that was 99.25% pure

[edit] Electrolytic refining
The purest copper is obtained by an electrolytic process, undertaken using a slab of impure copper as the anode and a thin sheet of pure copper as the cathode. The electrolyte is an acidic solution of copper sulphate. By passing electricity through the cell, copper is dissolved from the anode and deposited on the cathode. However impurities either remain in solution or collect as an insoluble sludge. This process only became possible following the invention of the dynamo; it was first used in South Wales in 1869.


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## amosfella (Dec 16, 2011)

Just spitballing here, could one take gold plated copper, brass, etc., and melt it, and either flake it, or roll it into a fine sheet and sue this process?? Or would there be too many problems?? For, me, the furnace isn't a problem. All I'd need are a few pots or crucibles with lids and some bricks to break...


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## Geo (Dec 16, 2011)

amosfella said:


> Just spitballing here, could one take gold plated copper, brass, etc., and melt it, and either flake it, or roll it into a fine sheet and sue this process?? Or would there be too many problems?? For, me, the furnace isn't a problem. All I'd need are a few pots or crucibles with lids and some bricks to break...



there are many possible ways to do any one thing, but is it more efficient or more economical? there are much better ways of removing gold plating than melting the whole piece.


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## amosfella (Dec 17, 2011)

what methods would you recommend then?? For the number of pins, and other plated stuff I have, it would take a lot of nitric, and HCl to do the separation... Also there is a lot of plastic buffers that are a pain to get out involved... incineration would be needed at the very least, and with the equipment I have, melting is a very short step...


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## Geo (Dec 17, 2011)

a sulfuric stripping cell comes to mind first. i have run batches of one pound at a time in my small pyrex cell, it does build heat and the contamination is horrid but we are talking about reclaiming gold and not refining. the total process consist of slowly removing base metals until you have a pure precious metal. even though we strive for the simplest and quickest, sometime we have to add an extra step or even two when dealing with large or difficult to work with material. AP (acid peroxide) is another method of seperating copper from gold, its not as fast as dissolution by nitric acid but it is cheaper and more user friendly. i have run batches of AP with 5 pounds of plated pins + another 2-3 pounds of gold plated boards in one five gallon bucket at a time. the tin contamination was horrible but there again....


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