froot - 18-5-2007 at 01:32
My wife has recently started a pewter art hobby where designs are pressed into sheets of pewter by hand. Apon completion of the design the artwork is
artificially 'patinated' to give that antique look. The 'patina' she uses is a blue/green liquid that has a strong metallic smell, like copper sulfate
(which I've tried without success). It is rubbed on the pewter artwork and rinsed off leaving the desired finish which is then polished. I believe you
can get different patina solutions giving different colour finishes such as black, copper, silver, gold and so on.
Considering how difficult it is to find a reliable source for these concoctions, I was wondering if you may have any suggestions for formulating these
patinas at home and what chemicals I could try.
Mr. Wizard - 18-5-2007 at 07:14
The copper sulfate would have been my first guess. The color the 'pewter' takes is largely dependent on what it is made of. If it contains a lot of
lead it will be darkened by one thing and if it's got a lot of tin it won't. High levels of lead are not healthy for serving or preparing food. You
didn't say what the pewter product was. Do you know the composition of the pewter you are using?
A friend was casting toy soldiers out of lead, melted wheel weights, actually, and had run out of the material he had been using to darken them. It
was a product used to darken leaded glass window came. I guessed it was a copper compound and made a small amount for him by heating a bit of copper
wire in a small test tube with some NH4NO3. Looking back it wasn't the safest thing I could have done, but it did make a great stain for the soldiers
after dissolving the purple material in water. One more thing, try warming the metal you want to darken. Put it in an oven on low, 200F or 100C would
be about right and then try applying the copper sulfate. The warming was needed even for the commercial product on the lead windows.
Edited for spelling 
[Edited on by Mr. Wizard]
Pyridinium - 18-5-2007 at 07:20
A couple of good ones for patinating pewter are HNO3 and so-called 'liver of sulfur' (don't use these together).
Liver of sulfur is a mixture of K sulfide and thiosulfate, I believe.
EDIT: I found a couple other recipes on finishing.com (begin copy & paste):
Jan 12, 2003
Instead solution from my first letter(which is simple and indigrient is easy available) you can try one of this two recipes:
BLACK FOR TIN
molibdenic acid........7,5 gm ammonium chloride......3o gm
H2O..........1 lit.
Hot immersion(60-80 C)
black for tin 2
bismuth nirate........5 gm
nitric acid..........50 ccm
tartaric acid.........80 gm
Goran Budija
- Zagreb, Croatia
[Edited on 18-5-2007 by Pyridinium]
enhzflep - 18-5-2007 at 07:22
Couldv'e sworn I had a section in one of my books on just this topic. No matter, I've just found a pair of recipes on the net.
For black patina:
Add some copper filings or thin copper wire to around 10% nitric acid 90% water.
For dark gray patina:
use around 10% sulphuric acid 2% nitric and 88% water. Always add acid to water, (I'm sure you knew that) and you can use the nitric-copper mix for
etching the pewter too.
They're from http://www.ganoksin.com/orchid/archive/200411/msg00323.htm
froot - 18-5-2007 at 11:39
Thanks for the replies. Apologies for the omission Mr Wizard, the pewter she uses is lead free, I'm assuming it has a high tin content in the alloy. I
did find that 'finishing.com' website and did take notes from there, although they have more info on the hot method. The patina solution she has been
using is applied at room temperature and works in seconds. I will try the simplest formula first and see how it goes, copper and HNO3.
Thanks again.
Eclectic - 18-5-2007 at 12:34
It might be copper selenate solution. If so, it will blacken steel at room temperature also.