Troubling Iridescence with Liver, Ferric, Copper
I've been trying to learn how to repatinate old copper (c.1900) using Liver of Sulphur [affil. link to product info on Amazon] and ferric nitrate. I've used "Contemporary Patination" [affil. link to book info on Amazon] (Young) and "Colouring, Bronzing & Patination of Metals" [affil. link to book info on Amazon] (Hughes) as reference.
Now and then, things progress exactly as I'd like, but I don't know whether these intermittent successes are more related to the actual alloy or something that I've done (or not). I'm trying to be as scrupulous as I can in preparing the surface using a commercially prepared cleaner that contains phosphoric acid.
My main problem is that the application of liver (either hot or cold) degenerates into a rather opaque coating of iridescent, metallic appearance. Typically, after the initial warm, coppery deposit, a bright gold forms followed by a magenta and then cyan coating.
For those not familiar with the original brown finish used on Roycroft copper, imagine the patina on a 100 yr-old hammered copper lamp...very heavy, almost black deposits in the recesses of the hammer marks with a warm, lighter brown revealed on their high points. I've been trying to build up most of the density I'd like with the liver to avoid having the entire effect become too red thru the use of too much ferric.
In short, is this iridescence that I'm encountering typical of the process and, if so, how do I avoid having it happen?
- Collingswood, NJ
I am similarly trying to restore the patina of a Stickley hammered copper bowl. I have ordered the books you mentioned and have had some success with online research. I am presently acquiring and testing all known techniques and chemicals. I have not tried ferric nitrate yet, but it is on the list of tests. I will test everything and then decide whether or not to go with Michael Adams' Aurora Studios repatination services. If you really want to have it done "right," his company is knowledgeable of the subtle differences between early and late finishes of Van Erp, Stickley and Roycroft metalwork.
Regarding your iridescence, I have a similar problem with some of my blackening chemical reactions- such as a "bluing" like gun barrels. I can knock that down a bit if I abrade the surface with ultra fine scotch-brite. I am also going to try Rottenstone [affil. link to product info at Rockler] and olive or Linseed Oil [affil. link to product info at Rockler] on a felt covered block. Though I have not tried it, one other idea is that perhaps the final step of wax polish (turpentine and bee's wax) will reduce such colorations.
Good luck and keep posting on your progress or with any tips you have for my restoration.J. McGowan
- Huntington, New York