Expert: Mike Fulcher - 12/11/2006

Question
Hi Mr. Fulcher,
I'm an antique dealer who works with archaic bronzes and other metals
frequently.  Lately, cleaning coins for non profit sale for our local
Chinese New Years event, I came across some detailed conservator set ups
for electrolysis.  However, in all the research I could find, spot
treatment to minute areas seems neglected.  this would be invaluable in the
treatment of "bronze disease", the formation of cuprous chlorides,
which is a fairly serious problem.
I tried using small cotton balls dipped in sodium carbonate solution
... but I am still not getting the accuracy I would like.  Is there a way
to gel a 3%-5% solution, or to gel an alternative solution for this
kind of application?  Preferably using commonly found items?  I was
thinking carrageenan, but I am not sure the effect it would have on the
electrolyte.
The coins were a gross experiment .. I am working on the amp per cm2 formulas I have read, but I think that the ability to use a steel probe
tip as the anode would be the best method, and the ability to use higher power and 'zap' the effected areas would be both time saving and be less destructive than typical mechanicla methods. Any recommendations specific to the questions or in general would be appreciated.
On a side, but related note ... I have some 200yr old iron pieces with hammered gold that is primarily covered with corrosion.  Would submersion electrolysis remove the gold?
thanks.
Nathan  

Answer
Nathan

Thanks for the question.  Oddly enough, I have some related past experience, where I was trying to make a gel that I could use to selectively plate copper to make wire traces.  What I ended up using was polyethylene oxide (and water) as my gel material.  It stays relatively thick without hardening, and was fairly easy to work with.  As it is water soluble, anything else you throw in there should mix right in (like the sodium carbonate).  You can purchase PEO from www.alfa.com.  It comes in different molecular weights, with the higher weight giving you a thicker gel from what I can remember.  I think for what you're doing it would be best to stick to 100-300,000 MW material.  100g will cost you $25, and should be enough for you to experiment with.

Your selective method using a probe might also work, but that will definitely be something that will take a steady hand.

As for the electrolysis and gold I'm not sure, but I wouldn't think the gold would be effected.  It might peel if the substrate beneath it is dissolved, but it should not go into solution.

I hope this helps.  Have fun with your project.