I checked and found out the Karo brand corn syrup is correct, rather than sugar. The purpose is to keep the zinc deposits finer grained which should help brightness. There is an ingredient in the Karo that helps this, but it's not the sugar.
Here is a better recipe for electrolyte than the link above.
Mix together 300 grams of Epsom salts, 100 grams of zinc sulfate, 200ml of white vinegar and about 1/3 bottle of Karo into 4.5 liters of tap water and stir.
You can buy 2 lbs of zinc sulfate for $9 with free shipping on ebay. An electrolyte will not plate zinc until it contains enough zinc ions. You will eventually put zinc ions into the electrolyte if you keep on plating long enough without the zinc sulfate, but having it speeds up the process. Tap water is fine for this as minor impurities don't matter.
140mA per sq. in. is the optimum current for zinc plating. A battery charger has relatively high enough amperage (maybe 2 to 10 amps?) that you need to be plating quite a few parts at once to get the optimum current per sq. in. of surface area.
To find the area of your parts, you can make some short cut area calculations for shapes like bolts, nuts, washers, etc. in a spread sheet and input their dimensions. After you have done a few area calculations a pattern will emerge with average, big, and small bolts, nuts, screws, and washers.
To find out the amperage of a battery charger requires some care. Most multi meters are capable of measuring only a very small amperage. Too much current and the meter will fry. AMHIK. A safe way is to measure the voltage and ohms of resistance and derive current by the formula I=E/R or amps=volts/ohms. The amperage of my battery charger varies with load, so the real output in a plating setup has to be determined. To calculate the amps output of a 12v battery charger, you will need to find out the actual voltage which is probably going to be something like 13.5v.
You can also use other smaller power supplies. The voltage does not matter at all for plating, only the amps. An example is a transformer from an old modem or router with input 110v AC and output 6v DC/750 mA. This unit should do for plating about 5.3 sq. in. of parts, which should be a lot fewer parts than with a battery charger at 2+ amps.
You can definitely plate one small part with a 2+ amp battery charger, but getting closer to 140mA per sq. in. will improve results.
Using correct amperage, it will take maybe 10 total minutes of plating time for most parts. Two or three sessions of plating work the best. At third time intervals or when the part looks blue-gray, wear rubber or vinyl gloves, remove, rinse, scrub with a brass wire brush and toothpaste, rinse in alcohol, and resume plating. Position the part differently relative to the zinc anodes each time to prevent "shadows" or unplated areas. When finished, clean the part with a brass wire brush and toothpaste again. You can polish with fine steel wool and toothpaste if desired. Rinse in alcohol.
It's best to have a good supply of cleaned up parts on hand before you start plating. I like to clean the parts with vinegar, but you can media blast also. After degreasing with dish soap, hot water, and a tooth brush, I soak in vinegar for quarter or half day increments until the fastener is bright and clean. Then I hand steel wire brush each fastener all over for a minute or two on a wooden board wearing a leather glove. You can store the parts in denatured alcohol to prevent flash rusting until you have a big enough batch to start a plating session. In case of flash rusting, dip briefly in muriatic (hydrochloric) acid, rinse, and plate.
DIY plating is not speedy, but it can save money, and you will have control. Local commercial platers want a minimum batch fee of $70. But what if you find some more parts that need plating after the first batch is done? With a home setup it's easy to plate one more part. And you can plate in multiple small batches as your restoration progresses.
After plating, you can dip the part in chromates of yellow-rainbow, black, green, blue, and olive drab to match the color of the original part. These are available from Caswell or you can make your own yellow-rainbow Cronak as mentioned above. Note that "clear" or silver colored zinc parts are dipped in the blue chromate. The blue is so subtle that most people don't see any blue. Next time you are in a hardware store, look for the bluish tint on clear zinc plated fasteners. The purpose of chromating is to temporarily prevent white rusting of the zinc plating. In other words, chromates may stop corrosion for only a few years or less, so it's a good idea to wax your newly plated and chromated parts for more protection.
