A hard, flat backup plate with fine grit carbo paper (like 600) lightly wet-sanded will usually brighten the ground without dipping into the embossing. Don't just wrap the paper around, or it might wrinkle enough to mess up the letters -- glue it onto the backing.
If the plate is dented, it won't work in the dents.
My backhoe has an aluminium serial number plate. The letters are lightly embossed and inked. I'd like to clean it up a bit. Can anyone think of a chemical which will clean the surface without removing the ink?
Chris, I've "been there done that" and I think the only thing you can realistically do is to mechanically remove any paint drips (I used the edge of a credit card) and then gently clean the surface with detergent/water, and that's about it. If your lettering is black & background gray (grey in Britspeak) you can fix small gaps in the lettering by using a sharp felt pen (in the US we have a wonderful product called "Sharpie" - I bet most metalworking shops now use them). In areas where there isn't any lettering, you can try lightly rubbing with fine steel wool. It appears to me that your lettering is simply inked onto a flat surface, so once it's gone it's gone. Another thing you can do since you've gone to the trouble of pulling it off, is to do a high resolution scan of the plate and try reproducing it somehow. There are lots of approaches to doing that.
Blimey Chris, If my dream came true and >I< had a JCB the last of my worries would be the s/n plate probably be far more worried by rusty door bottoms, leaking hoses, worn pivot bushes, bent forklift bar, jammed extradig etc etc
If you want my advice on the subject of buying one...
If you want one to use, spend the extra money and buy a good one to start with. Mine is something of an eternal restoration project. There are a hell of a lot of things to go wrong with a JCB. If you're seriously looking to buy one I can suggest some of the likely faults to look out for.
I came within a few thou of generating a good excuse to buy one when we were buying a farmhouse and land earlier this year which would have needed a fair amount of groundwork. We pulled out at the last minute when it turned out the seller was a crook and half the buildings had no planning permission and were set to be demolished by the Council ! When the move was 'on' I did a lot of homework on JCB's and came to the same conclusion as you. Was aiming for a 5 year old 4WD 3CX with extradig and 4 in 1.
Contact JCB, and have them print you a new one. Betcha it wouldn't be more than a double saw-buck, just because THEY would like to see the machine spiffed up. You might have to send the old one in, so they don't suspect you're stealing a machine....
The alternative is to buy an old machine with non of these things fitted. My 1963 MF65R is somewhat basic with no cab, forks, extradig, etc. It's interesting to own but obvoiusly lacks the usefulness of the later models. It depends on how much you will use it. I bought mine some years ago for some work which it did and I've never quite got around to selling it on.
In answer to the OP, I own an old car with aluminium number plates which I clean regularly. My answer is to ignore any damage to the paint and repaint when I've cleaned the ally. Personally I get them in the sink and scrubb with domestic scouring powder such as Ajax. A coat of black on the low bits takes some time but it looks really good afterwards. I suppose the plate should be laquered afterwards to protect it. That's something I've never done though.
In that case, google for "aluminium serial plate". There are a number of companies that will make one off's from your own artwork. A photo of the original can be re-touched in paintshop and copied onto the ally. Most seem to work on a surface print or an anodising system so the detail won't be recessed. Might be worth a look though. Don't know the cost.
That would be a sound choice for the job if you've got the money to spend on it. There are a few things I don't like about the modern machines. They have too much in the way of electronics and plastic. I hate the plastic cab roof, for example. That said, the newer I-section chassis is better designed and more fatigue-resistant than the old "Hydrachassis". But if you need a cheap machine, a 1970s 3C or 3D in good order will work great for a self-build.
Looks to be screenprinted not acid etched and filled. I have made thousands of these plates and many repros. The serial numbers are engraved so they will be ok. Get as perfect a digital image as you can and clean it up in photoshop. You can rescreen it or there is an easy way to make a waterslide decal if you have a laserprinter. Print it onto the decal paper. Very lightly spray the print with clear laquer. This might take 8-10 coats. once that is all very dry soak it in water and apply to the more cleaned up plate.
Funny thing is, I did meet a guy with a mint 1960s JCB which he'd acquired as a true rust bucket. He showed me a "before" picture of the machine and it was brown all over - hardly a sign of paint anywhere! The restoration was a real credit to the owner. Anyway, he let me have go and I noticed a pair of mint specification plates in the cab. So they are available from somewhere. I doubt he blagged them from JCB though...
Grab some Mothers mag/aluminum polish. Warm it up some so it isn't real stiff. Use a tissue or VERY SOFT cloth to apply it to the plate. Once on wipe GENTLY around all the areas with paint, try not to damage the paint (it should be ok but why take chances) Once you have it cleaned up good, carefully wipe off any excess. Mothers is a polish with wax in it but for better protection I would wipe it with wax/grease remover and spray it with some clear lacquer.