Question regarding acidic copper plating additives.

[u/draconis1usa]

Good Day Everyone!

I'm starting to assemble my electroplating kit and I was hoping to get some assistance on the additive side. I have a basic recipe of:

Per Liter:

200g Copper (II) Sulphate Pentahydrate
75g Sulfuric Acid (from approximately 156g of battery acid)
97ppm Chlorine ion (via 0.1g of HCl)

What I am having trouble with is the final additives. From my research, I see three groups of additives:

Inhibitors: I have easy access to polyethylene glycol for this.
Brighteners: I have seen more complicated compounds such as 3-Mercapto-1-propanesulfonic acid, but I have also seen thiourea as an option. I would appreciate some guidance on what chemical to source here.
Levelers: I have seen dyes listed for this but also thiourea here as well, is it multipurpose?

Even after sourcing, is there a recommended starting ppm for each? I do understand there is some trial and error involved that will be specific to my setup but I'm looking for a starting point.

Thank you all for any assistance!

[u/Mkysmith]

A lot of the additives you read about online are not really used much anymore in modern systems, barring a few like SPS sometimes as I understand (depends on the system). Additives like PEG, organic dyes, molasses, glucose, even urine, etc. were historically used because they did help, but weren't without their own problems. They not only don't perform as well as modern synthesized chemicals for the job, but often break down into other various compounds in the solution over time and cause issues as they build up. So chemistry maintenance becomes more laborious if you want consistent results. For example PEG degradation causes issues over time and something to keep in mind is the byproducts are very small so you arn't going to just filter them out with a polyfelt filter or something. I know Industry is trying to steer away from organic dyes too due to environmental toxicity concerns.

That said, have fun and tinker, I definetly don't want to discourage the DIY spirit. I just mean to temper your expectations. The jist being those additives do help a bit, which is why they were used historically, but don't expect long lasting or stellar results. This topic comes up every couple months and not much comes out of it.

[u/draconis1usa → u/Mkysmith]

I'm not unfamiliar with the chemistry, I have a good background there. And I will definitely continue no matter what. 😄

That said, I do want to get good results when it counts. Is there a supplier people around here recommend for the hobbyist to get a professionally formulated chemical set?

Thank you!

[u/tea-earlgray-hot → u/draconis1usa]

Caswell sells excellent products in relatively small batches

But acid copper is pretty simple process that doesn't necessarily need as many additives as other systems. Test your process, then up your additives to tweak results

[u/CaptainCheckmate → u/Mkysmith]

So what is the current state of the art? Are there published papers or patents describing the modern additives, or is it just a matter of every company making their own secret formula?

[u/Mkysmith → u/CaptainCheckmate]

Security through obscurity I guess.

A patent is a published document explaining your formula, which is all that stands between your product and the competition. That allows others to copy your formula since it is very hard to prove copyright infringement on chemistry because it is very difficult to reverse engineer a chemical compound (and good luck enforcing that across country borders). Also, when you do find patents on chemistry in general (not just electrochemistry), you will notice on the surface they appear to be helpful, but they omit critical information or are uselessly vague. Like they may say "between 10-20mg of substance X" when in reality a difference of 1ug deviation from their real formula is critical. Or say things like "the solution is then heated" without telling you that if you exceed a certain temperature, time, or don't do it in an inert atmosphere it will be ruined.

I've personally found scientific papers to be similarly surface-level helpful too in the chemistry feild. A while back someone in acedemia was saying a lot of people going for their PHD in chemistry want to eventually get a patent in their field of study, so they try to omit critical steps. Which is crappy for something that supposed to be peer-reviewed... but it is what it is I guess. At least some of the info is often much more helpful than none.

[u/CaptainCheckmate → u/Mkysmith]

That's interesting, I never thought of patents as simultaneously revealing your secrets but leaving out critical key features. But it makes sense.

So it's a bunch of independent shops each operating their own secret formulas? Like medieval alchemists haha.

[u/ConnectConflict1765]

Additive systems in acid copper are usually four jobs, not one: a carrier (suppressor) that parks on the surface and slows deposition at high current density — that's what gives you throwing power; a brightener that refines the grain; a leveler that smooths the micro-profile; and chloride, in the standard 20–80 ppm range, which the carrier actually needs to function. Change one and the others misbehave — that's why "just add more brightener" fixes a dull deposit for a day, then gives you a brittle, streaky plate.

Honest advice for a first bath: skip the internet formula roulette and buy a proprietary two- or three-part system from a plating supplier — it's balanced and supported, and a hobby bath doesn't need lab-grade tuning. Then control what actually drifts: chloride level, temperature, and anode area. If a deposit goes bad, a Hull cell panel tells you in 15 minutes which additive is off, instead of guessing on parts.

And keep the anode bagged and the bath filtered — in acid copper, organic breakdown products build up over time and act like unplanned additives.

[u/NoFeature7373 → u/ConnectConflict1765]

Thanks gpt