(taken from information provided by one of our clients and adapted for Caswell PRODUCTS)

POTMETAL. MAZAK. ZINC DIE-CAST.............the words that brings tears to a platers eyes and groans from his mouth. Its the metal from hell!

Potmetal is a slang word for a zinc based alloy that was used to form most of the trim parts on cars and motorcycles up into the 70s and in some countries beyond that time. Zinc in itself is a little difficult to plate. Then add 40 or 50 years of sitting in the weather, low current density areas that collect the rain, snow and pollution and you have a recipe for hair loss when you try to plate it! The only thing that can make it worse is if you happen to be working on a part that came from a Chrysler product that had a 12 volt POS. ground. That set up turns all of your trim into anodes! (I know, I have a 55 Dodge)

Well in spite of the difficulty, it can be plated. I wont say that I have the best method, but, I'm pretty sure it ranks up there with some of the best. Plus, its simple to do. No cleaners or cyanides involved.

Over the past 4 years I have worked with a lot with pitted pot metal.  It is probably one of the hardest metals to plate.

The process I use has had many refinements and changes. This is the best one I have come up with so far but is always open for improvement.  You can change it to fit your needs if that's what works for you.

1. If the part is greasy, degrease it by scrubbing it in a hot dish of Caswell SDKLENE-416.

2. Dry it off

3. We have 2 ways of doing this. First is to sandblast the part very, very well. You will be stripping the old chrome off, cleaning out the pits, and scouring the surface of the part to give the initial strike plate a nice surface to plate onto.  The alternative is to strip the old Chrome in a Caswell Chrome stripper and then use the Caswell Dry Pickle No. 4 to remove the old zinc plate and clean into the pits and scratches

4. When you have made sure EVERY pit is clean you can then sand blast the part to ensure that no old zinc or cadmium is left on the part.   If there is a small bit of black in the pit it will cause your plate to blister in that area later on.  

5. Next I will sand any casting lines off and shape the lumpy areas if needed. I use 80 grit sandpaper for this. You can also file if needed. If you have any cracks, "V" them out so you can solder them later.

6. Once the part is at this stage I dip it in SDKLENE-175 which is a mild caustic cleaner. Dip the part for about 30 seconds. This will turn the pot metal black. It seems to neutralize any corrosion in the metal and I have yet to have a blister after plating using this method.

7. Rinse well. Let dry. I put mine in the oven at 200 deg to speed it up if needed.

8. Now activate the part using the SD Pickle No4.  This will remove the blacking and also the oxides that wil be on the surface of the metal.

9. From this point on DO NOT touch your part with your bare hands. Use nitrile gloves. Rubber gloves leave residue on the part.

10. Put the hanger on the part that will hold it in the tank.  Sometimes I put it on prior to the last sandblasting. You will also want to wire up any robbers or auxiliary anodes at this point.

11a. Now I go into my Low Acid NICKEL STRIKE bath live. By this I mean with the power on and hooked to the NEG bar. Lower the part into the bath. I set my voltage at a very high setting initially so that the plating will get into the low current areas. Lift the part out every 15 seconds to make sure you're not burning any of the high current areas.

11b. You can use the Flash Copper approach for this action if you are not using a very low acid nickel strike coat.

12. If you start to burn (and you will) the high current areas back the voltage down about 2 volts. If you see dark spots showing up in the low current areas turn the voltage up. Once you do this about 10 times you will start to understand how to make it work. There's a learning curve on this so practice on some scrap pot metal and NOT YOU'RE PARTS!

13. Once you get the plating going at a nice dove gray color leave the part in for 15-20 min. This will give you a nice strong strike plate on the part.

14. After 15-20 min in the strike bath take it out and rinse it well.

15. Plate in the acid copper for 20-30 SECONDS...yup seconds. Why?  This will change the color of the surface so when you start to solder in the next few steps you can see where you're soldering. If you go the Flash Copper route you will not need this plate. It's hard to see your solder on a gray back ground like the nickel. I will sand the part with 100 grit sand paper to remove the copper, this way all of the pits are now a nice contrast of copper with the top surface in nickel.  Don't plate a lot of copper on the pot metal. What happens if you do is you will have a temp. difference between the copper and the pot metal that will be too great as you heat it up to solder it will start popping the plating and blistering it. Very depressing!

16. Pull the part out, rinse and let dry.

17. If the surface turns all different reds, purples, and blues, you can sand it lightly with some sandpaper. It will make the pits stand out.

18. If the part is big, I will put it in the oven at 300 deg to heat the whole part up. That way you're not putting a propane torch to it for a hour trying to heat it up. Small parts can be heated up with a torch.

19. Once the part is hot, start filling the pits with solder.

TECHNIQUES FOR SOLDERING

This is a list of things that I have learned over the years on how to solder pitted pot metal. Don't despair when you get blisters on Pot metal. It is probably the hardest metal to plate. You will have lots of learning experiences, but, hopefully this list will help.

1. If the part is long and skinny, trace it out on some paper first. The heat from soldering will warp the pot metal and this way you can bend it back into shape after you are done soldering.

2. If the metal is very thin, be CAREFUL not to heat it up too hot and drop it out on the floor. VERY DEPRESSING! There is a very, very fine line between melting the solder and melting the part!

3. On thin parts heat a small area and solder it. Then move to the other end of the part and solder it. That way you don't overheat the part.

4. I use a torch with Propane gas in it to heat fat big parts.  Once I get to the small thin areas I have a little butane pencil torch to work those areas with.

5. For small pits and thin metal use a thin solder

6. For big fat parts use a thicker solder.

7. Heat the fat parts first and solder them. This will allow the heat to transfer out to the thinner parts as you're soldering.  Once you start on the thinner parts the fat part will start to cool and draw heat from the thin areas helping to keep them from overheating.

8. Keep the flame of the torch moving. Don't concentrate it on one area. You run the risk of melting the part down if you do.  Remember Zinc (pot metal) melts at 785 F. Your solder melts at around 400F. That's not much of a window to play with. Practice on some scrap before attempting to work on good parts.

**********************************************************************

20. Once all the pits are filled with solder then you have to get the flux off. If it is a water based flux simply rinse under hot water.  If it is an acid/resin based flux you will have to take it off with a MEK or another type cleaner.

21. Now your part should look like something that fell out of the sky. Time to start sanding....

22. I start with 80 grit and then move to120 grit. If after sanding with the 120 grit you see some more pits then make sure to fill them.  You don't want to have to solder after you have a thick plate of acid copper on. Your part will blister badly.

23. Sand down again and repeat the above steps until the part is smooth.

24. Rinse and activate the part with a mild activator. Remember your dealing with zinc. Use the Pickle No4 for this purpose.  A green scrubby works well to scrub the surface with the activator. The problem area where you may get blistering will be the old nickel. So, scrub it well.

25. Now you're ready to Re-Strike the part in your strike bath. Give the part another 20 min. strike, rinse and go into the acid copper for 1-1 ½ hours.

26. Rinse the part and sand with 120-220 grit.

27. Activate and replate in acid copper for another hour.

28. At this point if your can sand with 400 grit and get the part smooth, then do it. If you still have some small pits then sand with 320-400.

29. I always like to put about a half hour of acid copper on at about 3/4 the normal current after this for buffing.

30. Sand with 400-600 grit and buff your part.

31. Clean, activate, and plate with nickel/chrome.

Start out with some small pieces of scrap copper, brass, and steel. Get a feel for plating and UN-plating them. Then move on to Potmetal. Find some old scrap pieces and practice like heck on them. Try plating, un-plating, buffing, sanding, soldering and different temp/amperage settings. Get to know how the baths work and why different things go wrong before tackling any real parts. Understanding why things work the way they do is a big factor in eliminating and trouble shooting problems. Believe me its a lot less frustrating!!

The project piece is well corroded and pitted.	Clean up the surface by grinding, sanding, or bead-blasting. Next drill out the pits as a dentist would do to a rotten tooth. Make sure you get all the black out as it can come back to haunt you later!!	Inspect the part over and over to ensure that it is ready for the next process.
The Zinc Die-Cast has now to be activated. After washing in the SD-416 alkali cleaner and rinsing in de-ionised water, the part can be immersed in the SD-Pickle No4 tank for activating. Rinse thoroughly after this treatment in de-ionised water.	Into the Flash Copper ™ tank  for about 30 seconds. Just enough so you will see the solder on the part. This is an alkaline copper which will not dissolve the Zinc and will give a good even strike coat.	The alternative is to plate into the low acid Pot Metal Nickel tank.  You will now be able to solder the damage.
Once you come out of the copper you can use lead-free solder. If it is a big part put it in the oven at about 300 deg. prior to soldering. Works Well!	Once all the pits are filled and the part its sanded/buffed smooth plate again with the Flash Copper Tank for about 15 minutes.	Rinse and into the Acid Copper Tank for about 45-90 minutes because you will be buffing next and Acid Copper will give a good malleable plate for  this process. If your a heavy hand at buffing then leave it in longer.
Buff the copper to a high shine and inspect to ensure you have not buffed through to the Zinc Metal If so its back to the Flash Copper Tank. Then degrease and clean. Get it ready for the nickel plate.	My cleaning (degreasing )set-up consist of a old waffle maker and my cleaner. The solution is on the right. I heat up and degrease in the cleaner, then wash with tap water, pickle if needed, then wash in acid neutralizer or caustic soda, next I wash with tap water, Finally I wash with distilled water and then to the proper plating tank.	Now into the nickel bath for about 20-30 minutes. It should come out nice and smooth and a dull to semi-shiny gray.  If you want added wear protection plate for 60 minutes
Buff the nickel to a high shine. This is where you get the base for the chrome plate. If you see defects here they will only be worse after the chrome is plated.  Take your time here... if needed go back and solder, plate with Flash Copper, Acid Copper, buff, nickel plate, and then buff again. Degrease the part in he SD-Klene416 tank and clean it up for the chrome bath.	Chrome plate WARNING!!! **DONT BREATHE THE MIST OR GET THE ACID ON YOUR SKIN!!!**Have a fan blowing the mist away from you or a vacuum cleaner exhausting the mist through a filter to atmosphere..	This is just a brief over view of how I do my potmetal plating. I left a lot of the cleaning between steps and buffing out to simplify it. If you have any questions just fire off a E mail to me and I will be happy to answer them.