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Zinc plating Steps

Updated: 2009 Jul 22

Always test with a few old nuts and bolts you don't care about first. It will give you a feel for the process and you won't destroy any real parts in the process.

Here are the steps involved:

1. Parts preparation. This step is critical to success and can not be overlooked. Failure to properly prep the parts will result in poor and/or spotty zinc adhesion to the substrate. This step is time consuming and not a lot of fun, but it is necessary. Basically, you must remove all paint, grease, and dirt. Clean it until you would eat with it, then wash it with soap and water, rinse and dry. The acid in the etching bath will not etch oil or paint covered steel. Also, you do not want to contaminate your baths with nasty chunks that will then get stirred up and land on your parts, resulting in poor plating. Don't cut corners here.
2. Hang the part. I start by hanging each part from a length of copper wire. Some parts are easier to hang that others because they have a natural location for hanging. Very small parts, however, are more difficult. But, I just bend the wire into a shape by the part can be supported and call it good. Do be careful not to drop parts into your bath. I can be a challenge to get them out…and a long magnet you don't mind getting ruined is a great help when fishing them out. I know some people have used small metal baskets to handle the tiny parts. I haven't had very good luck with this method because I get a lot of shadowing (uneven coverage) during the plating bath.
3. Etching bath. Suspend the part from a length of copper wire in the etching bath for 1 - 4 minutes. It may bubble in the beginning and then stop bubbling after a while once the original zinc has been removed. When I get going on a small run, I hang a number of parts on the side of the bucket.
4. Pre-plating rinse. Immediately after the etching bath, rinse the part in the pre-plating rinse at least 30 seconds. Essentially, you remove the part from the etching bath and immerse it immediately in the pre-plating rinse. If the part is oddly shaped or has compartments, be sure to move the part around in the pre-plating rinse to fully rinse the acid from the etching bath. Do not touch the piece with your gloved fingers…only handle it by the copper wire. If you touch it, it gets a trip back to the etching bath. When I get going on a small run, I hang a number of parts on the side of the bucket.
5. Plating bath. Immediately after the pre-plating rinse, immerse the part in your plating bath. Hook the copper wire over the copper pipe that is sitting across the top of your bucket.
   • The negative wire from your power supply will be connected to the copper pipe.
   • The positive wire from your power supply will be connected to the zinc anode (which is also at least partially immersed in the plating bath).
   • The zinc anode and your suspended part must not make direct contact.
   • Turn on your power supply and you will start to see bubbles come up to the surface as the zinc ions are being transferred from the zinc anode to your part (the cathode).
   • There are specific amperages and durations that can be calculated for the surface area to be plated on each part. Honestly, I've never bothered to figure this out. I do know that the amount of time (unless left plating for way too short or way too long) has not made an appreciable difference in the quality of zinc coating I've gotten.
   • About half way through the plating, I flip the part around 180° and hang it on the other side of the copper pipe. In doing so, I'm attempting to get even coverage on the part and prevent “shadowing” where one side is plated much more thickly than the other side.
   • How long do I plate? Well, it all depends on how large the piece is. Small pieces may only require 30 seconds. Large pieces as long as several minutes. Don't be afraid to pull the part out of the bath and have a look. You can always just drop it back in. After just a little while, you'll get a feel for how long it takes to plate the pieces you are doing.
   • With large pieces, I do them one at a time. But, if I have numerous small pieces (small nuts and bolts, etc), then I'll do several of them at once.
   • Before I begin and every few minutes thereafter I stir the chemicals in my plating bath. Perhaps this is normal or perhaps I used too many chemicals or not the correct chemicals or whatever, but my zinc oxide and molasses tend to settle at the bottom. So, I stir them up and keep my bath nice and cloudy.
6. Final rinse. Immediately after the plating bath, immerse the part in the final rinse for 30 seconds. The purpose of this rinse is simply to dilute the chemicals from the plating bath.
7. Dry. Towel dry each piece immediately after the final rinse. Don't be surprised if your towel gets a little gray from the extra zinc that didn't adhere fully. But, you should be left with a nicely plated piece. Set the piece aside to fully air dry. I like to place each piece - not touching - on a long piece of plywood. The wood absorbs any moisture and the separation of pieces prevents spot rusting. You could also just hang them up all around your garage, etc.

The good news is that if you make a mistake, you can just start right over again with the etching bath and run the part through again. The nice thing about zinc plating is that it is pretty forgiving.

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