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Old 31st Jan 2019, 2:31 pm   #71
Catkins
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Join Date: Feb 2015
Location: Chepstow, Monmouthshire, UK.
Posts: 234
Default Re: 1938 Murphy A56V television restoration

Apologies for the delays in posting, January is a busy month in work, as I have to travel to Brno, Czech republic for conferences and meetings (posting from Brno airport now).

Anyway, the last post mentioned there is a way of plating without grinding down to good non-pockmarked metal. That is perhaps obviously by building it up to a good surface by repeated plating and polishing. Obviously this is difficult to do especially with hard metal like zinc and nickel. So the way of making this work is to plate with copper, which is soft.

But you can't plate with copper directly over steel, as it will react. So first you must plate with a 'flash' layer of nickel, which doesn't react with either steel or copper. Then you can plate with copper, polish it down, and repeat. The more you repeat this, the better the finish becomes.

All in all I made about 5 to 6 plates of copper, which gave a good mirror finish. Photos 1 - 3 shows some of the progress, the finish getting better. The first photo shows some plating "burns", this is normally unwelcome because it gives a poor finish but here it is an artefact of doing a longer plate than normal, to produce thick plating. As the plating will be polished down it doesn't matter.

Once the copper plating has been finished, you can put a final plate of nickel on top, which looks OK. But I personally found zinc produced a less chrome looking finish than nickel. As zinc will react with copper (to produce brass), you have to first plate with nickel anyway, and then add a final layer of zinc.

In photo 4, the left bracket has been nickel plated, the right has had an additional plate of zinc. The bluish tinge is due to passivation.

Photo 5 shows a collection of replated metal components.
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