Zinc Plating Parts

I recently had a batch of parts zinc electroplated and am very pleased with the results. 

Shiny!

You have probably noticed that a large number of the bolts, nuts, washers and brackets on your car are gold colour. Or at least that they have the mottled and rusty patina that suggests they might once have been gold.....

Searching for 'gold'

Can you see it?

Back in the day, it was common practice to for such fixtures and fittings to be electro-plated plated in cadmium to provide a rust resisting layer. Very much in the same way that many bolts are shiny silver colour - 'BZP' - or 'bright zinc-plated'.

While a non-plated bolt will do the job just as well (and a stainless steel bolt will do the job even better) lots of D owners like the look that a little gold gives them under the bonnet. 

Attention to detail: Len Drew's car

I'm definitely not aiming for a concourse standard restoration, I'm happy for my car to look it's 54 years, but I would like it to to look a good 54, not a poor 54.

It's possible to get parts re-plated, just as it's possible to get parts re-chromed. However cadmium plating is all but banned or discontinued these days due to the toxicity of cadmium. While it's in the air and in the food we eat and is in things such as rechargeable batteries, it's pretty nasty stuff. It's the vapours and dust that are harmful and it's associated with lung cancer. Though it is still used in some industries, it's not really suitable for the hobbyist. The alternative is too go for zinc electroplating plating, finished with a yellow/ gold passivate. Cadmium is closely related to zinc and is found in zinc ore.

At it's most basic, the zinc electroplating process involves a small electric current being passed through an electrolytic solution (a conductive solution with free zinc ions). The negative terminal of the power supply is connected to the thing to be plated (so it needs to be able to conduct electricity!) and it is suspended in the solution. The positive terminal of the power supply is connected to a zinc bar. The current causes the zinc bar to slowly dissolve and the liberated zinc movs through the electrolyte to collect on the surface of the item being plated. 

The basic plating process
(image copyright - Mammoth Memories)

 

When zinc plating, initially the parts will come out bright silver, however a short dunk in 'yellow passivate' leaves them looking gold. Other passivate colours are also available.

Some caveats: Firstly, electroplating is not a magical restoration solution. It can restore the LOOK of a part, but not the part itself: a rusted and pitted bolt will still be pitted after plating. In fact the acids need to clean parts for electroplating may well leave the pitting and part looking worse than you thought it was. Secondly, electroplating will not last forever. It will provide added corrosion resistance and remain yellow for some time, but will eventually fade or corrode itself - just like the original cadmium finish did.

Notice that the pitting remains....

There are any number of small businesses that do plating and they will mostly be happy to take business for car and motorbike parts. Plating can be expensive - or at least prices can vary wildly - and, to get the best value, you really need to take a large number of parts along and negotiate a price. As I worked into my restoration, this didn't suit me for three reasons. Firstly there is HUGE variation in the size and shape of the bolt and washers used around a DS and I didn't want to muddle parts up. Secondly I was doing a gradual rebuild and I didn't want to have to strip everything just to amass a suitable number of parts to make plating worthwhile. And lastly I was reluctant to entrust valuable or hard to come by parts to strangers.

So....I started out by home plating with a DIY kit. This meant investing in appropriate chemicals, containers, pumps, heaters, thermometers and a power supply. There are starter kits readily available from websites and through Ebay etc.

Example of a DIY starter kit

The chemicals are only part of the cost. You also need to factor in pumps, heaters and the power supply. Others have gone into this big time and have set ups I can only dream of. Or I can visit their websites:

A semi-industrial set up
(photo copyright Citrothello)

My set up was more modest.....

Plating in the garden shed - 2016

New workshop, same set up - 2018

Home plating was very involved considering the small batches I was plating. It involved warming chemicals and using small pumps to get them flowing. The during of plating is important, as is the duration of the passivation process that leaves the parts gold colour. The cleaning and preparation was laborious but was a crucial part of the job. As was the de-greasing. Everything has to be hung on wires. That said, initial results were very good.

Zinc plating carburettor parts - 2018

Before plating

After DIY plating

.....but gradually my chemical bath turned dirty and soupy and the results were unpredictable. This was almost certainly down to a lack of maintenance of my chemicals on my part, but was indicative of the time and effort that needed to be invested, just to plate a handful of screws every now and again. 

Soupy......

There were several parts I wanted to plate that I always knew were going to be too big or awkward for my home set up. Keen to see how a professional plater compared to my efforts, I searched around and eventually found a plater in a nearby town. The price they quoted was significantly higher than I thought it would be but, for pieces that I could not plate at home, I felt I had little choice.  And I was curious! Looking at what I got back, the results were okay.......

A batch I had plated by a professional - summer 2019

.....but they lost a few small pieces. Nothing important but it said something to me about their quality control. I went back and they managed to fish a couple of missing bits out of their tanks - but they were so corroded they were unusable . 

These used to look quite good!

All in all it was an expensive and disappointing experience and I decided I would not use them again. As my rebuild continued, I went back to my DIY set up but the results were hit and miss. Plating continued to bug me and, as I was close to putting the car back together and wasn't willing to have the scabby old parts staring up at me from the engine bay, I knew I would have to bite the bullet one day. 

My car is a 1968 model and so the threads on the M5 bolts and nuts are 'ISO' standard 0.75mm pitch, not metric standard 0.8mm pitch. At the beginning of this year - and with reassembly firmly in sight - I was able to buy a number of old Citroen stock M5 bolts of the right pitch. However some were gold - cadmium plated - while others were plain black. When i bought them I had expected them all to be gold finish.

M5 set screws. 0.75mm pitch, but black.....

These proved to be the trigger for re-investigating zinc plating. I realised that I had so many parts still to be plated, that I couldn't do it at home. It would slow my overall progress. I decided to commit to farming the work out to a professional plater. Searching again, I found a plater on the other side of my home town. Less than 15 minutes away! Had I missed them first time around? Were they a new business? I think I had tried to contact them before never got through by phone so assumed they were out of business. I managed to speak to someone this time around and they were willing to take on the job.

I knew that any negotiation over price would be dependent on the number of parts I offered up, and that they would need to see the parts in question. It was going to be a difficult equation: finding enough parts to make plating worthwhile, but not so many that the total cost was crippling. So, with that in mind, I set about amassing all the parts I could think of that were going to need plating. That took a long time.....

As I have dismantled my car over the years, I have stored parts in more than 50 different boxes. Plus various nooks and crannies. And the attic. Oh, and the garden shed. I don't think there are parts under our bed anymore. While I maintain a reliable spreadsheet of what parts are in what boxes, I still needed to hunt through them all to find the bits to be zinc plated.

Needles in haystacks

Then, as I was removing the relevant parts from the boxes, I needed to keep a note on my spreadsheet of what had come from where so I could put them back in the right places after plating......

Some parts I wanted to plate were still attached to other parts that didn't need plating - so further searching and disassembly was called for. 

Some dismantling was needed

Air horn bracket. That'll want plating.......

These extra pieces needed to be added to my database and a note made that they had been removed for zinc plating..... Eventually I got a good pile of parts together.

A lesson I learned from my DIY plating efforts was that the finish you get is only as good as the preparation. While the platers will use a chemical 'pickle' to clean the parts, this is mostly to remove grease, not the crusty scale from corroded cadmium. So, everything was degreased using Jizer, grouped, then counted and photographed.

Cataloguing. Notice the traces of cadmium remaining on some parts

Then, in batches, I cleaned everything on a wire wheel. This removed crusty scale and any remaining traces of the original cadmium coating. I reasoned that the platers probably wouldn't and couldn't do this (time is money after all) and so if I wanted good results, I would need to put some effort in. Remember that Cadmium is nasty stuff, so it's important to wear a face mask if you choose to do this.

These are all the parts I amassed. The majority were going to be gold - yellow passivate - but a few were just going to be shiny silver finish. Allowing for the wheel nuts, bolts and washers in bags, I think there were many, many pieces in this pile as I took to the other plater several years before. There were at least 500 bolts, nuts and washers.

Ready for the plater

I found my local plater really friendly and helpful and I'd be happy to go to them again. He eyed up all the parts and gave me a price that was less than the price I'd paid several years previously, for more than double the parts! So the price was right, and the results were great too! Not a single one of the 500+ bolts, nuts and washers was missing, and they had all been individually hung from wires for the plating process. That's a lot of time and cost right there. 

All done!

I really am pleased with the results. And I'm sure all the effort I put into cleaning all the parts beforehand added to the quality of the finish.

Before

After

Also, the effort I put into getting to this point, should pay me back by virtue of a more straightforward assembly process - all the cleaning has been done. I'm sure as my build continues, I will find a few parts that I missed and should have had plated, but I'll cross that bridge when i come to it.