It’s satisfying when you strip something old and worn apart, refurbish it and paint to look like new. But it’s really disappointing when you have to re-fit or re-assemble stuff with manky old nuts and bolts. You could buy brand new fasteners of course, but invariably you can’t get them exactly in the style you want. For example most Japanese cars use M8 bolts with 12mm heads rather than the usual off-the-shelf M8 bolts, which have 13mm heads. Manually cleaning them up is very time consuming and doesn’t replace the original finish. Painting them is not really an option, so what to do? Recently, I tried out a method for restoring fasteners, and the good news is that it not only looks great, but is quick and easy to do as well. The method I used is metal blackening. This imparts the black finish that many new fasteners come in. It can be done at home and doesn’t require any special equipment. Industrial metal blackening kits are pretty expensive (£800+) but Frost do a small DIY metal blackening kit for just £35, and if you prepare the items correctly, this will give a professional looking finish.
The first step to refurbishing your fasteners is to prepare them. To show how the whole process is done, I’ve used a set of bolts for the SSR wheels I bought recently for my Mk1 Civic. These were originally blacked when new, but were now pretty rusty. They were also a bit oily from the penetrating oil I used to remove them, so the first job before I could de-rust them, was to de-grease them. I put them in a sealed container with some brake cleaner and gave it a good shake. Drained off and dried out they could go on to the next step… de-rusting.
Cold metal blackening is only suitable for ferrous metals (but not stainless steel), so the chances are the items you want to restore will be rusty. For metal blacking to work effectively, you want them to be clean bare metal. In the past I’ve used brick cleaner for this purpose. Brick cleaner contains phosphoric acid which will dissolve the rust leaving just bare metal. A far better way I have found is to use a product by Chemodex called Rust and Scale Remover. This is also phosphoric acid based and works very well, but is stronger and thus faster acting than brick cleaner. It’s not cheap though at £51 + VAT for a 25 litre drum. For smaller jobs you can just buy 5 litres for £15 + VAT. Soak your items in this stuff until all the rust is dissolved. Fasteners that have any Cadmium or Zinc plating will fizz like mad in this and make it go frothy so make sure the container has enough capacity for the froth to not overflow. This stuff is also pretty nasty so wear gloves! I found that 3 or four hours is enough to see most rusty fasteners clean. If they are really bad you may have to take the worst ones out halfway through and give them a scrub with a wire brush before chucking them back in. Ideally, when your done stripping the rust, you want to be able to rinse the parts off in water and go straight on with the coating before they have a chance to rust again. Be sure to keep and eye on them though… leave them in too long and once the rust is gone the metal is self will start to slowly dissolve!
The metal blackening kit itself consists of three main chemicals. An alkaline degreaser, the metal blacking solution and a de-watering oil. The blackening process creates a porous base that bonds chemically with the surface of the metal. The chemical Blackening compound is copper/selenium (CuSe). The black coating by itself wont stop the corrosion… that’s where the oil comes in. The de-watering oil finds its way into the pores of the black coating, where it is held in close contact with the metal surface. It’s the oil that prevents air and moisture from reaching the workpiece surface and thus prevents corrosion.
The blackening process itself is pretty straightforward. First you need to prepare and areas to work in. This needs to be warm, ideally above 20 degrees centigrade. The three chemicals are poured into the three containers supplied in the kit and arranged in the process order… Alkaline degreaser, then blackening, then de-watering oil. You will also need a couple of buckets of water for rinsing. The rinsing is to limit cross contamination between the chemicals so you rinse after degreasing and again after blackening. I placed a heater under my little work table which warmed the tubs of chemical. It seems that if they are a little warm the process works really well. Again, you want to be using gloves for this and, in case of splashes, you really should wear eye protection too. I can’t imagine any of the three chemicals would be much fun in your eye! When you have your bare metal fasteners ready to go, you just need to follow this procedure…
- Place the items in the alkaline degreaser for about 10 minutes. If there’s likely to be air pockets anywhere just give them a stir round a couple of times.
- Remove them and rise thoroughly in you first bucket of water. Shake off any excess water when you remove them. A sieve comes in useful for this.
- Place the items in the blackening solution for 3 to 5 minutes but NO MORE. I found 3 minutes was enough with the solution warm. It will take longer if the solution is cold. It worth giving them a couple of stirs again.
- Rinse in your second bucket of water. Shake off any excess water again.
- Place the items in the de-watering oil and leave them there for 10 minutes. Give them a stir and a few more minutes then remove.
- Lay the finished items out to dry. Don’t wipe them dry as this can compromise the final corrosion protection.
Here’s all the nuts and bolts for my SSR split rims finished and looking like new…
And that’s it! Easy huh? Of course this process can be used for anything made of ferrous metal so you could re-coat all the metal clips and brackets in you engine bay for example. The other beauty of blackening is that it’s great for precision components as the coating is only about one micron thick. It can also withstand over 570 degrees Centigrade so it’s quite tough too!