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Old 15th Jul 2019, 4:51 pm   #1
Welsh Anorak
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Default Zinc passivation

I'm hoping to restore a tatty Garrard 301 turntable. The linkages are badly tarnished, and I believe coated in a toxic plating. Most specialists who restore these to a high - and expensive - standard talk of replating by zinc passivation. Anyone know a place that would do this? It's only a small quantity of levers and linkages so I doubt would interest an industrial firm.
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Old 15th Jul 2019, 6:03 pm   #2
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Default Re: Zinc passivation

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Originally Posted by Welsh Anorak View Post
Most specialists who restore these to a high - and expensive - standard talk of replating by zinc passivation.
Glyn, as far as I'm aware, passivation of zinc is what happens when galvanised (zinc plated) iron slowly oxidises. If you try to paint galvanised iron while it is still bright, the paint will quite quickly peel off, leaving an ugly mess. If the zinc plating is allowed to oxidise slowly and form a matt patina, the paint will stick to this much better. This is why you often see street lamps, roadsigns and other street furniture made of galvanised iron remaining unpainted for a while.
It could be that there is another process, though...
Colin.

There's some more on this topic in this section. See the thread "Zinc Plate and Passivate? Restoration".

Last edited by ColinTheAmpMan1; 15th Jul 2019 at 6:09 pm. Reason: More info.
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Old 15th Jul 2019, 6:09 pm   #3
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Default Re: Zinc passivation

You can do it yourself. Look at this company specialising in classic car stuff, they sell the kits.

https://www.frost.co.uk/zinc-plating-modules.html
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Old 15th Jul 2019, 7:41 pm   #4
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Default Re: Zinc passivation

At this moment, I cannot open the Frost link, but I'll check it again later.

This term "zinc passivation" cropped up in a thread a few moths ago. I believe it (usually) refers to the practice of plating a metal first with zinc and then putting a chromate coating on top of the zinc.

As chromates are now known to be highly toxic, they are being used less than they used to be. Having looked at any and all threads about plating which have come up on the forum, my impression is that it is getting progressively more difficult find the sort of small plating shops who are willing to take on small odd jobs.

I'm now starting to experiment with nickel plating, having been involved with that in my day job back in the 80's. As is frequently the case, getting just the right appearance with any form of plating often involves a bit of luck.

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Old 15th Jul 2019, 7:43 pm   #5
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Default Re: Zinc passivation

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Originally Posted by ColinTheAmpMan1 View Post
Glyn, as far as I'm aware, passivation of zinc is what happens when galvanised (zinc plated) iron slowly oxidises. If you try to paint galvanised iron while it is still bright, the paint will quite quickly peel off, leaving an ugly mess. If the zinc plating is allowed to oxidise slowly and form a matt patina, the paint will stick to this much better. This is why you often see street lamps, roadsigns and other street furniture made of galvanised iron remaining unpainted for a while.
It could be that there is another process, though...
Colin.
In metallurgical terms passivation refers to the process whereby a metal surface becomes more passive, i.e. less prone to corrosion. This can be as you say an oxidation process whereby an oxide film builds up and protects the surface or it can be a process of adding a protective layer but generally when people refer to passivated zinc they mean an additional protective layer, usually a chromate based process, that is carried out after the zinc plating. A good example would be the yellowish colour that you often see on plated nuts and bolts, this is a type of passivated zinc finish.
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Old 15th Jul 2019, 9:16 pm   #6
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Default Re: Zinc passivation

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At this moment, I cannot open the Frost link, but I'll check it again later.
No rush, they're out of stock!
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Old 15th Jul 2019, 9:53 pm   #7
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Default Re: Zinc passivation

The examples I've seen have been a nice bright gold colour, similar to the original, though toxic, chromate finish. Sounds like the nuts and bolts Paul's referring to.
I'll look into the Frost kit - they're a reputable firm so I'd expect good things of it.
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Old 16th Jul 2019, 6:12 am   #8
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Default Re: Zinc passivation

Yes, Frost has been going many years, starting originally in the US I believe. Their prices cause a young Yorkshireman like myself to take a sharp intake of breath! The quantities of chemical included in their kits often look like there would appreciably more than you'd need for a 'one-off' item

The passivating solutions to go with zinc plate don't mention chromate, and I'd guess that they probably don't utilise chromate, especially for a DIY kit.

From what I could see, there are no formal Safety Data Sheets (i.e. MSDS as were) directly on offer on the website. I'd guess that they must have to supply them, but may do so quietly, as those sheets often contain info that might be of interest to competitors.

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Old 16th Jul 2019, 6:15 am   #9
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Default Re: Zinc passivation

There are several DIY plating kits available - there's one from a firm in Bath. A web search will help you.

We use nickel plating at work - it's a 5 litre tub with the necessary chemical solution, some zinc supended in it and a small power supply. It works very well but we only do small items like clarinet keywork. We have sone silver as well, that's a little more difficult but a good finish is possible.
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Old 16th Jul 2019, 6:58 am   #10
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Default Re: Zinc passivation

I've used one of the DIY plating kits from Frost (years ago), it worked well, but required a lot of careful preparation - fully 'stripping', polishing (as in drill mounted polishing mops & pastes), and degreasing of the parts to be plated. To achieve a high quality finish is similar to good paintwork, the secret's in all the prep work before you start plating.

The obvious alternative, especially if it's a one-off job, is to use one of the smaller companies specialised in classic / vintage motorcycle restoration. I've had the usual array of levers, brackets, etc. replated (chrome) in the past, as well as more sensitive parts, e.g. the reflective interior plating on a '40's 8" Lucas headlight (bright nickel ?) - all came back with excellent results, with the plating company often preferring to do the prep work themselves. There used to be an advertising newspaper called 'Old Bike Mart' where all the specialists used to advertise, not sure if it's still going but it used to be like the yellow pages for bike restorers.

Alan
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Old 16th Jul 2019, 7:57 am   #11
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Default Re: Zinc passivation

https://www.classic-plating.co.uk/

https://www.gaterosplating.co.uk/

https://www.goldn.co.uk/

The latter two are suppliers I've used for DIY kits and can recommend.
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Old 16th Jul 2019, 8:53 am   #12
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Default Re: Zinc passivation

Zinc plate and colour passivate. This gives a finish very much like the old cad and pass.

If you can find a local plater that does this nip in and see the foreman early in the morning before the management get in, you should be able to get a few bits done for the price of a drink, rather than the official minimum charge which can be quite high.
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Old 16th Jul 2019, 9:31 am   #13
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Default Re: Zinc passivation

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I'm hoping to restore a tatty Garrard 301 turntable. The linkages are badly tarnished, and I believe coated in a toxic plating ...
It's cadmium.

If you're thinking of DIY zinc plating you may well need to get rid of the cadmium first. I fear that that could end up being the most difficult part. There are, as you say, specialists who can do it though.

When I had my 301 done by Loricraft, who at the time were the only people allowed to use the Garrard trademark, they explained that they keep a stock of re-plated linkage parts and they use those to refurbish customers' turntables. When they've collected enough cadmium coated bits they send those off for stripping and re-plating. I think they said they use nickel, but I wouldn't bet my pension on that.

I believe that SME have now taken Loricraft over and that as they start putting new turntables into production they will stop refurbishing the old ones.

Cheers,

GJ
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Old 16th Jul 2019, 10:03 pm   #14
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Default Re: Zinc passivation

Thanks for all that! I'm ploughing through it and I'll let you know how I get on.
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Old 17th Jul 2019, 1:18 am   #15
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Default Re: Zinc passivation

I had a bicycle frame zinc electroplated a few years ago. It gave it the yellow colour of the hardware shop nuts and bolts and the rust protection. It was something like 30 for the frame and forks. I looked in the Yellow Pages and there was a place on the local industrial estate.

If not obvious, ask around local painters (powder coaters/sprayers), steel factors or car repairers. They will certainly be able to put you onto someone who does metal finishing. It may seem like there are no people around who do this, but mainly that's because people just look online rather than asking locally. I can't think that if I were a plater I'd have a website - I'm an Architect and haven't got one! Word of mouth does for me, as for them so you may have more luck sleuthing that way.

In any case, talking to someone in the know is worth hours of trawling online, especially if you can show them the pieces you have in mind.
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Old 17th Jul 2019, 12:31 pm   #16
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Default Re: Zinc passivation

We get car components re-plated from time to time, usually in Zinc, chrome or gold passivate. The results can be a bit variable even from electroplating companies. Much depends on the condition of the parts in the first place.

We have tried two of the Frost plating kits (Zinc & nickel I think) but not the passivate ones. The results have been a complete failure. Having read up on other people's experiences, it seems there is a huge learning curve and lots of experimentation needed to get acceptable results. We gave up in the end!

We have tried several different platers in our area, and none have been willing to do odd bits cheaply. They all have a minimum charge of about 80 for which you can actually get quite a bit done. They are not interested in messing about with a couple of bits.

We now have to wait until we have a sufficient quantity to make it worth while.

All the best
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Old 17th Jul 2019, 8:23 pm   #17
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Default Re: Zinc passivation

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We have tried several different platers in our area, and none have been willing to do odd bits cheaply. They all have a minimum charge of about 80 for which you can actually get quite a bit done. They are not interested in messing about with a couple of bits.
This is the situation that has been reported in previous threads about plating.

When I was involved in plating at work, we used an 'electroless' nickel plating solution that was "infallible". I saw a baby's first shoe that was plated with that stuff. Unfortunately, the British company that made it was taken over by a foreign company many years ago and they either discontinued it or renamed it. I contacted them last year, but as soon as they realised I didn't need tonne quantities, they cut me dead.

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