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Extreme dilemma


#1

Dear Ganoksers,

I am at my wit’s end with a problem I can’t solve. I’ve been making some pendants of mixed copper and brass, expecting to move on to include silver once I have the step-by-step process for this particular design well-enough rehearsed in the less expensive materials. The exact design is not an issue. Basically these end up as hollow, round pieces about 2” diameter, shaped something like a lentil, that is, two shallow bowls brazed face to face. The two little bowl-shaped faces are made of copper and brass sheet, 1/32” thick. (I forget the gauge number) Working with flat sheets of copper and brass - They are first cut into simple matching shapes, like adjoining jigsaw puzzle pieces, for example, they are sawn out, the copper and brass shapes fitted well and brazed edge to edge with hard solder, then sunk, raised, and planished into a pair of little bowl shapes, their edges trued, the two bowls brazed together, convex-to-convex faces with ‘easy” solder. Tiny vents in the joined edges of the bowls allow for gas expansion. Quite attractive - the surfaces polished and the two-toned design shown by the two different coloured metals with a very fine line of silver (solder) between them - which looks elegant. Over time the ambient atmosphere and ordinary wear and tear cause the colours to change slowly, to evolve and i love the way they end up looking. Simple and lovely. I’ve made a few, as I say, just to routinize the process for myself. I have no formal training in this work but I’ve been doing it for sixty years, no doubt re-inventing the wheel countless times - just for fun.

So all went well until the last one I made - using the exact same materials, literally cut from the same sheets - and following the same process I’d worked out - when all was done, pickled, and polished, there was no brass colour to be seen. it was as if the faces were made up only of copper sheet. “Aha!”, I said to myself. “I know what to do!” My first thought was that I’d maybe contaminated the pickle pot with iron - the most obvious cause. I actually didn’t think that was the case because I’m careful about that. Also - what looked like garden-variety accidental copper-plating did not take on the solder lines, only on the brass. But just to be safe I dumped and replaced the pickle (Sparex #2) then re-polished the faces, going right back to 400 grit and up through tripoli and white diamond - thinking this was more than enough abrasion to take off any copper that had been accidentally plated onto the brass surfaces. But no! The whole newly-exposed surfaces still all looked like pure copper. ( except the silver solder lines, which retained their silver colour). I redid the whole process from the coarsest to the finest - beginning to worry about thinning the metal to where it would become fragile, but I was becoming a bit obsessive because i KNEW there was brass down below the stubbornly copper-coloured surface. There is no intrinsic monetary value to worry about here, and I’m very happy to totally sacrifice this piece to solve the mystery. I was beginning to doubt my sanity. No matter how I grind, scrape, sand, buff, it is as if the brass sheet has turned to solid copper sheet. A couple of commercial de-tarnshers and polishes have been no help. (Tarn-x and some other one I don’t recall) none of them get the brass back from wherever it hides.

I fell back on another pickle/clean-up recipe which my wife searched out - a mixture of white vinegar and hydrogen peroxide. That has produced some fascinating, and beautiful visible changes on the surface - both colour and texture affected - which i hope to study and exploit in their own right as design elements in future. For example the previously invisible patterns of blows from forming and planishing hammers have emerged - subtle like the stripes on a tabby cat - but it’s still all copper! What happened to my brass sheet?

This has not happened to any of the previous pieces. What has happened to this one?

Thank you for your suggestions, if any.

Marty Hykin, Victoria, BC, hobnob@shaw.ca


#2

I will follow this post closely as the same thing happened to me once. Usually the peroxide mixed 50/50 with regular pickle (called super pickle) does the trick in bringing back the brass but I have also had the rare time that it didn’t.


#3

Was this original sheet stock or was this newly ordered metal? Who is your supplier?

White diamond is still a polish. I would try using a 3M Unitized Wheel, med grit. They remove everything. Sandpaper should remove a pickle coating which is why I want to rule out a metal problem.

Pictures help here.

Karen Christians
Western Avenue Studio, #506
122 Western Ave.
Lowell, MA 01851
Karenchristians.com
781-367-4992


#4

It sounds like your pickle stripped out the zinc from the brass, at least on the surface. It’s like how depletion gilding works in gold alloys; the most reactive metals are leached away by the acid, leaving the least reactive on the surface. In this case, the most reactive metal in your brass alloy was the zinc. If you want to recover the brass look, you’ll need to grind away the surface until you get down to it. But actually, the surface effects you’ve accidentally discovered sound more interesting. Next time, if you want these to stay looking like brass, mix the pickle a little weaker, use it cooler, and don’t leave the pieces in too long.

Andrew Werby
www.computersculpture.com


#5

Hi Marty

I had a student come to me with the exact same issue. So we tried fresh acid and sanding which did improve things but not enough. So we next did the peroxide (9%) with acid which stripped the rose color off the work and restored the piece enough to pass her requirements.

I have found brass to be a great challenge in many instances especially brazing. Ask you supplier about the zinc content. I had successfully enameled on brass in the past when I was in the USA but I have recently had students really struggle with brass enameling here only to discover the zinc content is different in the UK.

I believe Andrew’s advice about the pickle is sound. I have learned a weaker solution and less time helps.

Good luck.

Rachel Hearne


#6

I have seen this before. What occurred to us was the torch was much hotter and pulled the copper to the surface. Instead of using polish to cut below the surface, try a fine file (on a small area) and then polish. Hope this helps.
Steve Ramsdell


#7

Thanks to you and all who replied.

I think the answer is mostly found in the excessive length of time in pickle pot. In retrospect I think a dinner break intervened and in that time stripped out the zinc to a much greater depth than I would have imagined.

We live and learn. One lifetime is not enough.

Marty