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Old 1st Apr 2019, 11:47 am   #1
Steve G4WCS
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Default Zinc plate and passivate? Restoration.

Picked up a "linear" amplifier.

Front panel looks OK and it needs a good de-dusting. but the back panel could do with a light restoration.

Is it zinc plated and passivated and is there a receommended method of restoration? I'm thinking alng the lines of some sort of coloured lacquer ( I'm sure you could get something similar for restoring the finish on carburettors ) rather than completely dismantling the unit and getting the panel re-plated.
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Old 1st Apr 2019, 5:07 pm   #2
Bazz4CQJ
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Default Re: Zinc plate and passivate? Restoration.

I'm not sure that I've heard of a passivation process being applied to a zinc coating. Perhaps more likely, the platers had some tricks up their sleeve to get a zinc plating with a specific look.

Most carburettors are made of aluminium alloys; I don't think I've seen one with zinc plating.

There are kits on the market to carry out plating by means of a cotton swab on the end of a graphite rod, that is dipped in a plating solution and then used to do electroplating. I've seen quite good results from them, especially when the area is small as in your case. They may well be worth a try.

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Old 1st Apr 2019, 7:58 pm   #3
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Default Re: Zinc plate and passivate? Restoration.

This was the stuff I was thinking of. Supposed to replicate zinc chromate

https://www.frost.co.uk/eastwood-bro...SABEgJfvPD_BwE
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Old 1st Apr 2019, 8:57 pm   #4
Bazz4CQJ
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Default Re: Zinc plate and passivate? Restoration.

So, the Eastwood stuff is an acrylic paint which looks like zinc chromate. I wonder how closely it will match?

If you are going to remove the existing zinc with carbide paper or whatever, I guess that will get you down to to plain steel. As you don't have endure the under-bonnet conditions of temperature and petrol, I wonder if you could find something cheaper than £16, perhaps something from the model paint people like Humbrol (who have a metallic bronze).

I'm not too sure that any paint will give a really close match to real zinc plate, but guess it depends on how demanding you are .

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Old 1st Apr 2019, 11:40 pm   #5
alanworland
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Default Re: Zinc plate and passivate? Restoration.

Unless things have changed I thought a zinc plated finish could either have a clear or coloured passivated finish applied?
Might be worth asking a platers

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Old 2nd Apr 2019, 3:26 am   #6
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Default Re: Zinc plate and passivate? Restoration.

Quote:
Originally Posted by alanworland View Post
Unless things have changed I thought a zinc plated finish could either have a clear or coloured passivated finish applied?
Might be worth asking a platers. Alan
A couple of moments on Google reveals that zinc platers do indeed use the term "passivation" to describe the addition of a chromate layer on top of the zinc layer.

The terminology is a bit loose; a more formal description of passivation is as per Wiki https://en.wikipedia.org/wiki/Passivation_(chemistry) but we start to get in to splitting hairs over passivation and inhibition.

For an object which lives in a environment which is not very corrosive, I think you'd expect standard zinc coating to be satisfactory.

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Old 4th Apr 2019, 8:47 pm   #7
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Default Re: Zinc plate and passivate? Restoration.

Linear arrived tonight. Opted for citric acit derust (lemon juice), Brasso, and hard paste wax.
Will do a restoration post in success stories if 80’s kit is deemed vintage / interesting enough
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Old 4th Apr 2019, 11:05 pm   #8
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Default Re: Zinc plate and passivate? Restoration.

That looks really good. A re-visit with the wax every blue-moon might well keep it that way!

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Old 6th Apr 2019, 8:21 pm   #9
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Default Re: Zinc plate and passivate? Restoration.

That's made a real difference - it's easy to see where the tissues were (I assume soaked in lemon juice?)
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Old 6th Apr 2019, 8:42 pm   #10
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Default Re: Zinc plate and passivate? Restoration.

Yes, an hour in lemon juice, brought the rust pits back to grey steel
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Old 7th Apr 2019, 12:28 am   #11
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Default Re: Zinc plate and passivate? Restoration.

Quote:
Originally Posted by Steve G4WCS View Post
Yes, an hour in lemon juice, brought the rust pits back to grey steel
And by "lemon juice" we really mean...citric acid, as I mention... occasionally

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Old 24th Apr 2019, 7:01 pm   #12
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Default Re: Zinc plate and passivate? Restoration.

My mother had great difficulty getting citric acid a few years ago for some preserves. The shopkeeper said that apparently there was some control of it because of its propensity to get cut with cocaine!
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Old 24th Apr 2019, 8:00 pm   #13
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Default Re: Zinc plate and passivate? Restoration.

Never had any problems, either on the High Street or ebay.

Used some citric yesterday to clean up a small mild steel bracket which was rusty in some places and covered with zinc plate in others. Cooked it up to about 50°C, and after about an hour, both the rust and the zinc were gone leaving a very a really nice surface to paint with primer.

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Old 24th Apr 2019, 8:40 pm   #14
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Default Re: Zinc plate and passivate? Restoration.

That's a good Linear I have one of those, very clean output and the preamps a boon
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