My last post on this subject showed the initial copper plating almost covering the graphite. An hour or two of further plating produced a nice bright copper layer over the entire surface of the rubber mould.

The plating was fairly smooth and seemed to be filling corners well. At that point I wanted to stop, or at least slow down, plating beyond the edges of the mat itself.

I coated the outside area with insulating varnish. This is an acetone-based varnish normally used when winding transformer and electromagnet coils to keep the wires from shifting and also for additional insulation.

Unfortunately this varnish turned out to have small pores in it. These were perhaps caused by residual water or electrolyte crystals on the copper when the varnish was applied.

In any case, further plating resulted in the growth of copper nodules (sometimes called “flowers”). I occasionally took the mould out of the plating bath and broke off the nodules, and even at one point tried another coat of varnish.

The actual mat seemed to be growing a layer of copper, but the inside corners were not plating well and were getting close to being closed in by the nodules growing along the upper edge of the mould cavity. This would leave water-filled cavities trapped within the copper. Because of this I stopped any further plating until I could get better control of the process.

Although they are a nuisance when plating, the flowers have a very fine nodular structure.These are some of the initial flowers shown alongside a dime.

This is how the plating looks now. The excessive growth along the edges of the cavity, as evidenced by the dark shadow along its top edge, threatens to trap water in cavities in the copper.

I have done some research on plating, and although it seems to be a somewhat black art, where every problem seems to be potentially cured by every fix, I have found four things to correct before trying to plate again:

1. During the days taken for the plating, water has been evaporating from the plating bath. When I returned it to its bottle yesterday, I found that half its volume had been lost.
2. I had started plating with an anode made for electroplating, but once that was gone I switched to using a piece of copper pipe, but this may contain impurities that could interfere with proper plating.
3. The anode naturally grows a layer of black copper oxide as it is consumed. This layer is consumed as fast as it if formed and so shrinks with the copper, but once all the copper is gone, there is a thin leaf of copper oxide left which breaks off and its crumbs can become distributed through the plating bath.
4. I had no agitation of the plating bath, so inside corners would naturally tend to contain stagnant electrolyte depleted of copper.

So my plans generally are to keep the bath covered most of the time to reduce evaporation, get some appropriately pure copper for the anode, put the anode in a cloth bag to confine the copper oxide that flakes off, and try using a small pump to spray the electrolyte directly against the face of the mat.

But for now I’m putting all that away so I can use the workshop to make some cases to contain all my new composition matcases.

My first attempt at making a rubber mould of a Lanston display matrix ended up with a fatal flaw due to an air bubble.

I made a second attempt, hoping to avoid repeating this flaw.

The instructions for the casting resin recommend applying a vacuum to the mould after filling it with resin in order to expand any bubbles, causing them to either pop or float up through their own enhanced buoyancy. I do not have a vacuum pump readily available so I will have to try pouring the resin very carefully and using a fine probe to poke around in all the nooks and crannies of the mat.

Having used the resin once, I decided that it was not necessary to seal the sides of the casting cavity since any resin leakage would be minimal. Sealing would probably still be needed if I were to use a vacuum to remove bubbles.

I also had a better estimate of the amount of resin required to fill the cavity, so I mixed less this time than last.

I poured the resin into the cavity of the matrix very carefully, allowing it to flow on its own along the contours of the type so as to minimize the chances of trapping an air bubble. I also used the tip of a fine copper wire to probe the perimeter of the cavity of the matrix.

The resulting cast was a success, with no bubbles around the letterform. As well, most of the dirt had been stripped off the mat in the first casting, so this one was much cleaner.

The colour balance of this photo is incorrect. This casting has the same pink colour as the previous one.

For the electrical connection for electroforming, I stripped the insulating varnish off some #32 magnet wire, threaded it through the edge of the rubber mould and along its surface, and poked the free end back into the rubber. This held the bare wire more or less in continuous contact with the surface of the mould.

Then I put some of the graphite powder we sell as a papermaking pigment into the cavity of the mould and overlapping onto the wires. I shook off the excess and used a small paint brush to brush off more of the graphite. The graphite is conductive enough to cause the copper to plate over the entire surface, and also acts as a release agent (although I’m not sure if that is necessary with this rubber).

The plating bath and copper anode I used also came from Lacy & Co. but the directions are pretty vague: use between 3 and 9 volts. I settled for adjusting the voltage to produce 200mA of current (this took about 2 or 3 volts).

After a few hours of plating, the copper had spread almost completely across the face of the matrix. A bit of the graphite is still visible in the middle. Another hour or two and that was copper-covered as well. The freshly-plated copper has a rather striking reddish colour, quite distinct from the copper colour one normally sees.

Once the surface was covered, the task remained to continue plating until the matrix was thick enough. Because of the plating characteristics of the copper, this is turning out to be harder than expected.

More on this in another post…