First of all, you have to make a copper-based solution
to apply later on the metal.
1 liter of distilled water.
25 gr of copper sulfate.
20 cm3 of sulphuric acid.
You have to dissolve the copper sulfate on the water and then add
the acid. Then, using a patch of fabric of a brush you just apply
it to the damascus blade. Good thing is that it will (kind of) respect
the finish of the blade, but with the typical redish tone of the
copper.
Once it dries, you can hand polish it or even use a soft belt on
it. On one blade, after the acid etch, I leave if a while on a 1:1
solution of water and clorhidric acid until the black residues of
the steel with more composition of carbon disappear. Then I apply
the copper solution and after that, I use a water 600 grit sandpaper
to remove it from the surface of the blade, leaving only the bas-relief
part of the blade covered with copper. (Picture 1)
On the other blade, the technique is easier, as I just apply the
copper solution after the acid bath, so the copper adapts itself
to the previous shades of the damascus, resulting in darker lines
where the steel was black. After that I hand polish the blade with
some fabric to get the final results. (Picture 2)
Note that both blades are made of the same damascus, and while the
scans and the colors do not match exactly, you can see that the
bas-relief parts of the first blade are the same color as the high-relief
parts on the second one.
One thing to note about this is that the copper just bonds with
carbon steels, not with stainless steels (or nickel, as I tried
this process on my "coin damascus" too and it didn't work
out well)
As the copper oxidizes with the carbon steel in a passive way, it
prevents the steel from rusting with the oxygen.
I tested this on a carbon steel ruler I used to use to measure the
forged blades on the anvil and while the non covered part got rusty,
the copper covered one did not. I don't know how rust resistant
it becomes, but it sure delays rust on the carbon steel.
I've been also experimenting with galvanic techniques for carbon
steels and now I use an electrolytic process based on cyanides and
the results are much better than the previous two other method I
just described.
This is a more complex process, but more importantly,
it can be very toxic, so if you're going to try this, please be
very careful. Do it outside or on a very ventilated place, using
gloves, as the products involved can be hazzardous for you health.
On the small scale that I use, I don't really get much fumes, but
still take that into consideration if you're going to do it.
For the electrolitic solution, I put a liter of destiled water on
a plastic or glass recipient and then I add 30g of copper cyanide,
25g of potasium cyanide, 15g of sodium carbonate and 2g of sodium
hyposulphite. (Picture 4 and 5)
I use a car battery (12V) with a charger, a variable resistance
and a voltimeter (tension=2,5-3V)
You can easily make a variable resistance for this process using
the wire nickel-chromium resistence of an old electric heater, serial
connected to the galvanic circuit, adjusting the clamps til the
voltimeter marks the desired voltage. (Picture 6)
The piece to copper gets connected to the negative and the positive
goes to a copper barstock/flat barstock inserted on the solution.
As reference, for a 6" blade I leave it 20 minutes at room
temperature. |
