[topfuel67]

I have searched for the correct way to finish the base, but keep finding different info. I recently invested in diy plating using a variable power supply and have plated all the linkage. Should the base be nickle plated and then dipped in black chromate? I've done a lot of my bolts in that and they're looking nice. It doesn't look like they were painted, but now that I media blasted them they are very light grey.

[Tom Vaught]

The bases I believe used a process from years ago called Black Oxide.
They were NOT painted. "Black oxide or blackening is a conversion coating for ferrous materials, stainless steel, copper and copper based alloys, zinc, powdered metals, and silver solder.[1] It is used to add mild corrosion resistance, for appearance and to minimize light reflection.[2] To achieve maximal corrosion resistance the black oxide must be impregnated with oil or wax.[3] One of its advantages over other coatings is its minimal buildup.[2]"

Hot baths of sodium hydroxide, nitrates, and nitrites[3] at 141 °C (286 °F)[4] are used to convert the surface of the material into magnetite (Fe3O4). Water must be periodically added to the bath, with proper controls to prevent a steam explosion.

Hot blackening involves dipping the part into various tanks. The workpiece is usually "dipped" by automated part carriers for transportation between tanks. These tanks contain, in order, alkaline cleaner, water, caustic soda at 140.5 °C (the blackening compound), and finally the sealant, which is usually oil. The caustic soda bonds chemically to the surface of the metal, creating a porous base layer on the part . Oil is then applied to the heated part, which seals it by "sinking" into the applied porous layer. It is the oil that prevents the corrosion of the workpiece. There are many advantages of blackening, mainly:

blackening can be done in large batches (ideal for small parts),
no significant dimensional impact (the blacking process creates a layer about a micrometre thick),
it is far cheaper than similar corrosion protection systems, such as paint and electroplating."

Rochester Products made millions of carburetors The process above was cheap, fast, able to do very large volumes of parts and offered a small amount of corrosion protection to the parts to make them look good as the carbs went out the door at the dealerships.

Tom V.

[topfuel67]

That's what I was guessing. The same thing they did with bolts. I'll try plating one of my extra bases then dip it in the black and see how it comes out.
Thank you for the info.

[Dick Boneske]

Yes, as Tom said, they were black oxide. It was a dull black color, but offers very little rust protection. I've been using Eastwood's Zinc Phosphate coating on carb bases. It looks very much like black oxide, but offers much better rust protection.

The first two pictures are of NOS Tripower carbs I have showing the black oxide bases. The last three pictures are of the Eastwood Zinc Phosphate coating I use. Note that it is very similar to the factory black oxide finish. When my '64 GTO was judged by GTOAA, the judges thought the bases were original black oxide but questioned why there was no evidence of rust.

[topfuel67]

Thank you for the pictures. I might try one in just etching solution as that comes out similar to the ones in your pics. I'll post photos of my results.

[Dick Boneske]

As you can see from the first two pictures above, the oxide coating was applied at the factory prior to machining, so there are several areas that have no coating at all. If you want exact originality, duplicating the machining marks would be difficult.

I've also used black oxide bolts for body assy. They rust the first time they're exposed to water, especially rainwater or condensation.

[topfuel67]

I found the same to be true with the bolts I did in the phosphate. That's why I invested in the plating. Plus I can do the gold coloring on parts that require that. I also found a satin clear coat rattle can. Its for car interior dash/plastic so it is flexible. It works good on protecting the phosphate finish and dries soft. It doesn't flake or chip and you can't tell it is clear coated.
Here are my first parts done zink plated and chromate dipped. The washer on the a arm rusted too much with the phosphate so I did it with plating.

[Jack Gifford]

For whatever it's worth- I found a cheap & easy imitation of black oxide finish; warm the [clean] part with a torch (but way shy of red hot) and dip it in motor oil (non-synthetic) and hang it to cool slowly. For heads of panhead screws in carb tops it looks just like original black oxide (at least it did for me). But it is also prone to rusting, like the oxide. I haven't tried it on a carb base.

[Blued and Painted]

Mr Jack, that sounds like a color case hardening process used on fire arms.
http://www.turnbullmfg.com/wp-conten...-home-full.jpg
I've used cold blue on some small pieces. I antiqued a new wing nut for the air cleaner. Also blued the distributor hold down clamp. It will eventually rust.

[topfuel67]

The method for using phosphate is pretty easy. I used etch and prep from the hardware store. Got a cheap electric hotplate a nd some 2 qt pirex measuring cups. 1 for the hotplate, 1 filled with acetone and one with distilled water. After sandblasting parts dip in acetone, then etching solution on med heat. Let bubble for 15 min or so, then dip in water, then acetone and use compressor air to quick dry. Looks like factory black for bolts, but does rust easily. The satin clear for plastics works good for rust prevention.

[topfuel67]

Just finished plating my first carb. I'll finish the other 2 tomorrow and hopefully the bases too.

[tempest1964]

topfuel, just curious. What was the do-it-yourself plating process you purchased?

[topfuel67]

It wasn't a kit, I reseached and followed what others did. The main difference in what I went with was I bought a variable power supply, volts and amps. A lot of people use battery packs, car chargers or tool chargers/transformers, but those seem to limit your options. You cant do a carb body with the same output as small brackets. I mixed in 4.5l distilled water-300g epson salt, 100g zink sulfate, 200ml white vinegar, and 5 oz karo corn syrup. Then used the swamp cooler zinc iodides and wired them to the power supply for the zinc plating. For the yellow or black conersion I bought the solution from caswell.

[tempest1964]

Very impressive.

[Dick Boneske]

Carb bodies were not plated. They were dichromated at the factory as the pictures show.

This process uses a chemical bath containing a chromium compound that is heated to 120 degrees F. into which the cleaned carb bodies are dipped for about 15 seconds to deposit the chromate on the surface.

Plating may look OK, but if originality is what you're after, the dichromate process is the only way to go.

[topfuel67]

What is in your dichromate bath? I tried using the ppg dx533 and then the dx503. The 533 worked great as a cleaner, but the 503 didn't do anything.

[Dick Boneske]

Sorry, I don't do the zinc dichromate in my shop. I have a local zinc plating shop do the dichromate process. Recently, the supplier of the dichromate bath changed their policy and would no longer sell the product in 5 gal. pails--would only supply in 55 gallon drums. Cost was prohibitive at more than $15 per gallon. He is now using an alternate source for the chemicals. I do not have the name of the product, but will get it next time I have carbs colored.

I know a person in Milwaukee who restores Quadrajets and does the carb bodies himself in his shop with yellow zinc plating. He has no legal way of disposing spent chemicals. I've had him do a set of Tripower Rochester carbs, but the result was far from the appearance of dichromating--too bright, too yellow.

The dichromate chemical is difficult to purchase because of the hazardous nature of the chemicals. The chromium content makes disposal a hazardous waste problem. Using this chemical in your home is highly discouraged.

[carbking]

Like Dick stated, you do NOT want to do the chromate at home, even if you can steal the chemicals!

This link to my website may provide additional information: http://www.thecarburetorshop.com/Carburetorfinishes.htm

When we were still restoring carburetors, we farmed out all of the chemical work. I don't have any brain cells I wish to waste on the chromate!

Jon.

[topfuel67]

I appreciate the advice and health warnings. I'll look into finding a plating shop to do the dichromate process. I'm in California, so I'll probably have to send them out. Everything is banned here.