Ferric Cloride and Copper

Forrest Taylor

Forrest Taylor

Knifemaker / Craftsman / Service Provider
Joined
May 13, 2021
Messages
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I have a copper spacer in a Damascus spacer and I will be etching the whole piece. Question is how will the copper react and should I coat it with something to protect it?

The ferric cloride is ordered otherwise I'd test it.
 
Copper will not react. But the ferric will be tainted with the copper and will leave a reddish tint on other knives when you etch them.
 
Jesse Latham said:
Copper will not react. But the ferric will be tainted with the copper and will leave a reddish tint on other knives when you etch them.
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Thank you. Good to know. Looks like I'll pouring out a small amount for the spacers.
 
Apply the ferric chloride to the spacer with a Q tip, or put a small amount in a container-and dispose of it when finished.
 
I'm confused by the responses, so maybe I'm not understanding the question. Ferric chloride is most commonly used to etch away unprotected copper from circuit boards. I would expect it to eat away at any exposed copper. You could protect the copper with the pens that are used to make circuit boards.
 
The dark aged look is not what I'm looking for I'm wanting the Damascus to be etched and the copper to still be shiny
I figured I was gonna have to mask off the copper with fingernail Polish or something like that
 
Longer term the copper will tend to darken like an old penny. When I did some tantos with bronze habaki, I preemptively darked it with cold blue. Darkened can be a nice look too.
 
Or you can resand after etching with fine strips of sandpaper.
Copper will darken, it won't stay shiny unless you cover it with lacker or so
 
Multiple comments:
The copper will be etched much more than the steel. It will turn dark. In my electronics days we made circuit boards by drawing the circuit on a sheet of copper covered phenolic with a sharpie and then eating away all the exposed copper with FC. Until recently, most folks go their FC for knifemaking from electronics suppliers.

The simple way to find out what the copper will do in FC is to test a scrap of copper in some FC. Use a small cup and not your whole FC tank. Draw several lines on the test sample with a wide tip sharpie and etch the piece. See how much eats away and what color it turns.

When a tank of FC gets a bunch of copper dissolved in it auto-plates it onto steel objects that are etched in the tank for a long time. This coppery color coating is very thin and will come off in clean up or with a quick rub with steel wool.

Copper won't stay shiny if exposed to air or use. It darkens into copper oxides which is the color of an old penny. I prefer using bronze when I use it as part of a guard, as it has a prettier brownish color when aged than copper. Both bronze and copper can be returned to shiny with a quick rub of a jewelry polishing cloth or a high grit 3-M cloth (pink. mint, or white).
 
I ferric chrloride etched some Mokume I made and it gave a rose gold hue to some damascus pieces (the brighter steels like 15N20) I etched afterwards. Oops! Now I save that container just for Mokume.
 
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The copper does darken a little but There isn't any noticeable difference in the depth of etch of the copper.
 
I should have said that a short etch on a knife will not make much difference, but a long or multiple etches may cut the copper deeper. When doing circuit boards the layer was about .002" thick and was gone in about 5 minutes.
 
The dilution of FC is probably the other difference. We etch circuit boards in straight FC.
 
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