Copper Rim Cap for a Drinking Horn: Etching, Electroplating and a 50/50 Acetone Secret

A father and son metalwork project — copper sheet, toner transfer etching, and one tip that will save you days of frustration.

My son is at university and his club has a drinking horn that's been in use for a couple of decades. It has a leather carrying strap attached to a couple of rings that we suspect are nickel-plated copper or brass. The two bands look like cast metal — the mould was some kind of Celtic or Viking knotwork pattern. Have a look at the photos and decide for yourself.

But the rim of the horn was becoming damaged and delaminating due to blows and general wear and tear. One option was to cut a few cm back to fresh material — but that road goes nowhere, and the new rim would just suffer the same fate. So we decided to take on a little metalwork and electroplating project.

Step One: Stabilise the Rim

Before doing anything else we injected epoxy between the delaminating layers of horn material, wrapped the rim in cling film, and clamped it between some curved blocks until cured. Once the rim was solid again we made a cardboard template of the inside and outside of the rim, about 2.5cm wide.

The Plan

The idea was to transfer the template to two strips of 0.8mm copper sheet and solder the ends of each strip together into two rings — I believe the term is elliptic bezel. One strip would be wide enough to cut a series of fold-over tabs along one edge; folding those tabs over the rim of the horn would pull the inner and outer rings into contact, and then we'd solder the tabs to join the two rings into a single cap.

First problem: raw copper sheet is work-hardened from the rolling process. It was stiff, springy, difficult to cut and almost impossible to form neatly. We needed to anneal it.

Annealing

Annealing is straightforward — heat the copper to red hot with a gas blow torch, then let it cool slowly. After that, the copper was beautifully pliable and a pleasure to work. We should have done this before we cut anything; it makes tin-snip cutting dramatically easier too.

Deciding to Etch a Pattern

Once we knew we could work the copper, we wanted to etch a pattern into the rim cap to match the existing carrying rings. So we tried several approaches to getting a resist layer onto the copper.

Photoresist film and UV light — total failure. We wasted nearly two days trying to get the exposure right and figure out a suitable mask. There are much better methods; don't go down this route.

The Toner Transfer Nightmare

The approach we kept reading about was to print the design onto paper with a laser printer, then transfer the toner onto the copper as an etch resist. We bought a cheap Brother laser printer for about £50.

Iron-on transfer — print the design, place face-down on copper, iron the back to release the toner. Did not work at all for us, though it apparently works for others. Complete fail.

Pure acetone transfer — print the design, place face-down on cleaned copper, wet with pure acetone and rub until the toner releases. We failed time and time again with every paper type we tried — glossy, cheap A4, magazine covers. The toner just wouldn't release cleanly.

We almost gave up. We were running on no sleep after several very late nights and it had been a pretty horrible time.

The Magic Trick: 50/50 Acetone and Water

Then I came across a comment in a video online. Someone mentioned that pure acetone didn't work for them either — but a cheap nail varnish remover had. What was different? It was diluted with water.

We tried mixing our acetone 50/50 with water. After days of failure, it just started working. It really was like magic.

The method: print your design onto cheap A4 paper (thin magazine pages would probably give an even cleaner result — smoother surface, better release). Place face-down on the copper, wet with the 50/50 solution and rub gently until the acetone evaporates. Then take it to the sink and rub under running...