|The MGA With An Attitude
CHROME PLATING -- UT-112
Technical Information supplied by M.J. Moore in Cheshire, UK
I spent over a year reading about chromium plating and making enquiries before taking the plunge and getting my windscreen, handbrake, etc. replated. At the outset I wondered what the engineering specification would have been for MGA plating and I found there existed a British Standard for Nickel Chromium plating, BS1224, originally written, I believe, at the end of the war, 1945. As plating technology advanced and scientific understanding increased over the years the original BS1224 was updated at intervals – 1953; 1959; 1965; 1970; etc. BS1224 was incorporated into a European Standard in 2000, BSEN12540 and, more recently, superseded by the current International Standard BS EN ISO 1456 – 2009. If anyone wants to learn more about Ni-Cr plating I would recommend reading up on this Standard. I would bet a hefty sum that BMC‘s engineering department would have drawn up a Ni-Cr plating specification based on BS1224 and specifically for MGA production this would have been BS1224: 1953.
I managed to get to read BS1224:1970. At the heart of BS1224 are four ‘Service Conditions’, one of which the plated article would see in its life:
SC 1 : Mild --- Articles used indoors in warm, dry conditions, e.g. radiator valves.
SC 2 : Moderate --- Articles used indoors but with some degree of wetness, e.g. shower fittings.
SC 3 : Severe --- Articles used outdoors in normal conditions.
SC 4 : Exceptionally severe --- Outdoors in severe conditions, i.e. salt, acid rain, cars!
For each of these conditions BS1224 gives the minimum thicknesses required for the nickel layer beneath the chromium and for the thickness of a copper layer beneath the nickel, if used, for two substrates, steel and brass.
The first point that stands out is how thin the chromium is : there appears to be nothing in the BS that considers thickesses other than 0.3 microns! The nickel thickness is crucial in giving reasonable corrosion resistance and for
steel substrates and the four service conditions the minimum nickel thicknesses required varies from 10 microns for SC 1 to 40 microns for SC 4. For a brass substrate the nickel can be reduced to a minimum of 30 microns.
Another interesting point is that if copper is used prior to nickel plating the nickel thickness can be reduced to 30 microns (steel substrate) but only if 20 microns of copper is put down. So this may indicate that copper is not used mainly to improve corrosion resistance but to give the possibility of ‘mush buffing’ where the soft copper is squashed into pits and scratches during the polishing process and to give a better surface.
So armed with this ‘specification’ of a minimum of 40 microns of nickel for steel parts and 30 microns of nickel for brass parts I had a look at my old MGA (brass) windscreen surround and an old MGA rear steel bumper. The Ni-Cr finish on both of these was poor and peeling off in places. I measured the thickness of some of the peeling plating and found that the windscreen plating was 50 microns and the rear bumper was 60 microns If the chromium is only 0.3 microns then basically these figures are for the nickel layers. Both of these original parts then were well within the BS ‘specification’ and gave me confidence that BMC probably used BS1224.
The next move was to find a chromium plating outfit that would plate my windscreen with at least 30 microns of nickel and I made a list of about ten platers from all over Britain and phoned each one asking how much nickel they put down. I was very surprised at the answers to say the least! Only two firms out of the ten actually knew about BS1224 and said they could plate to SC 4. These were Peacock and Trelfa in Scotland and Merridale Plating in Birmingham. Of these two the former told me that they had recently stopped plating parts for Classic cars and I got the impression that they found they were more trouble than they were worth. Merridale was a promising place and I made a mental note to take the windscreen there when it was ready. Several months later when I was ready I again phoned them only to be told, yes you’ve guessed it, they had stopped plating Classic car parts. I suspect that any plating outfit which is knowledgeable, efficient and perhaps with expensive diagnostic equipment and a state of the art plating setup will want a regular high throughput of easily jigged similar sized articles to plate and not say a radiator shell for a Lagonda one day and an MGA handbrake the next! The remaining eight plating shops were a mixed bunch and not one of them had heard of BS1224. Not only this but only one appeared to know what nickel thickness they used and at less than the 10 microns I was told this was much less than the ‘specification’.
One outfit with a very honest and pleasant boss basically said that they did Classic car parts but that they had the same schedule as other parts they did regularly which were clearly those subject to SC1 in use. Another guy when asked questions was convinced I was from the Inland Revenue and said that he plated motor cycle parts which ended up in a Motor Bike museum (SC1 !) and if they were happy then so should I be.
Because of this lack of success in finding someone to plate to specification I picked four outfits to give me quotes for plating the six main windscreen parts. I didn’t see the point in getting my Mazak grab handles replated and bought a new Mazak pair from Scarborough Faire. They were a bit fatter than the originals but not too noticeable. The plating prices for the six pieces (frame plus stanchions) varied from just over £100 to £370 and I chose the dearest (Derby Plating). I wasn’t 100% satisfied with the results (on Day 1) because the wire they had used to dangle one of the parts in the tank had been too close to the part’s surface and had caused a visible shadow on the chrome. What they will look like on Day 1500 will be anyone’s guess. They do, however, look beautiful on the car. If someone were to ask me however what extra I got for the £370 compared with £100 all I could say would be that maybe I’ve got a thicker nickel layer. Not very reassuring.
Derby Plating plate copper before the nickel but only on steel substrates. For brass parts they would leave out the copper.
As a final point it appears that in the most recent British Standard (ISO1456: 2009) they have added a Service Condition 5 for cars and boats which is the same as SC4 but with the stipulation that the finish should show no signs whatsoever of pitting or corrosion after a minimum of 10 years. For this the specification should include Duplex nickel plating (two separate layers of nickel ) and either microporous or microcracked chromium but not regular chromium plating. None of the platers I contacted could do other than regular chrome plating and only one did Duplex nickel (Niphos in Crewe).
To all those about to have some plating done perhaps it’s best to choose the most expensive outfit and keep your fingers well crossed! --- Mike