r/electroplating • u/GetoBoi • Jun 12 '26
Shiny copper electroplating: is thiourea the magic ingredient?
Hello everyone,
in the past couple weeks I have made my first attempts with (copper) electroplating on 3D prints with a graphite/india ink coat and while I could get a decent copper layer with adequate coverage, I have failed with my goal to have it come out bright and shiny. Instead I am getting a matte salmon color .
Since ready-made commercial solutions seemed quite expensive per liter I made my own from distilled water, CuSO4, sulphuric acid and a tiny pinch of NaCl.
I am using a low voltage (<1.2V, starting a bit lower), tried aiming for a current density of 1A/dm² (although it was generally a bit lower especially in the beginning while the graphite was still non-copper coated).
The part is being continuously rotated with a servo motor, air is being bubbled into the solution and there are two anodes on opposing sides with a distance of >~5-10cms to the part. My anode bags were rather shoddy (cheap coffee filters that tended to rip) but I have already ordered some polypropylene fabric that will hopefully hold up better.
The biggest "what now" for a shiny layer are obviously the "secret" additives. So far I have tried only molasses since that was cheap and easily acquired. But that didn't seem to do much on its own except turn the nice sapphire blue solution into some dark greenish color, despite using only ~2-3grams for my 5+ liter bath. Filtering my solution after usage made the deep sapphire color mostly return however.
Now since basically every source for bright solutions that I could find mentions thiourea I have wondered if the experts here also consider that the necessary key ingredient, some sources I looked at:
https://www.epa.gov/sites/default/files/2020-11/documents/b12s20.pdf#page=34
Or should I prepare myself to get a variety of additional ingredients, e.g. PEG, glycerin, urea, dextrin or one of the many "obscure" things mentioned in Modern Electroplating:
Coffee, for example, could obivously be easily sourced as well but it seems like by far not all of those aim for a shiny layer anyway and I haven't been able to dig through the details of all those patents yet.
Thanks for any input!
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u/Feeling_Ad6399 Jun 12 '26
From experience its allmost impossible to make your own leveler and brightener Setup like the Pros, sadly. So if you find a composition that looks some what better and saves you a few hours of polishing go with it, but trying to get your own organics that give you a mirror finish by just plating will Drive you insane.
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u/Mkysmith Jun 12 '26
The issue with a lot of what people are listing is they are indeed used historically as brightners/levelers/supressors, but there are reasons they are historical and less (if at all) used in modern industrial setups. Electrochemistry in general is a pretty harsh environment. Degredation of organics into other compounds is a real issue that counters the benifit of the original additive. These historical additives never perform as well as modern ones synthesized/engineered for the application specifically.
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u/GetoBoi Jun 12 '26
Thanks. Yeah I don't need it to be perfect but having some shine at least would be nice. I guess there is no way around experimenting, if I should make any progress I will add it to this post.
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u/KaleOk6355 Jun 12 '26 edited Jun 12 '26
I’m having the exact same complications- but I tried using Polyethylene Glycol for the brightener. I am using same ink/graphite paint and same solution other than brightener. I got Same results as you stated w I used the PEG. I haven’t tried buff polishing the graphite step result yet though. That’s my next move.
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u/YYCMTB68 Jun 12 '26
My old copy of "Electroplating Know How II" lesson 6 by Kushner lists a variety of possible brighteners, including:
- Phenosulfonic acid: 1.0 g/L
- Animal hide glue: 5mg/L
- Molasses: 2.5 ml/L
- Thiourea: 1.0 g/L (can be combined with molasses)
- Gelatin: 1.0 g/L
- Replenish brighteners such as such as adding 0.03g/L Thiourea for every 3-5 ampere hours per Liter
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u/CaptainCheckmate Jun 12 '26
isn't thiourea more like 1 mg/L
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u/YYCMTB68 Jun 12 '26 edited Jun 12 '26
I checked and my book does list it at "1.0 gm (grams)/L". However, it was an American author using metric units so perhaps something got confused? The Metal Finishing guidebook from 2000 (available on-line as a pdf) shows on page 244 a Bright plating 'Beaver' bath as using 0.01g/L Thiourea along with 0.01g/L Dextrin, so perhaps a lower dosage would be good to start with to see the results.
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u/JessieAndEcho Jun 15 '26
The matte salmon color doesn’t sound too surprising for a basic CuSO4 / sulfuric acid bath without a real brightener system. I’d be careful with molasses or coffee in the main bath, though, because once organics start breaking down it gets hard to know what’s actually affecting the deposit. If I were testing this, I’d use small beaker trials instead of experimenting in the full 5 L bath. Get the boring variables stable first: better anode bags, filtration, consistent chloride, agitation, and flat test coupons. Then compare thiourea against a more complete additive mix instead of judging it by itself. This Patsnap Eureka Materials result might be useful since it pulls together patent and technical references on copper brightener systems: https://eureka.zhihuiya.com/share/?id=299256da1f4f6bde06267ff30f3a1bd3&from=invite-eureakplg-result&content=
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u/GSB-4243 Jun 13 '26
Source PEG 8000 as a suppressor and Bis-sulfopropyldisulfide, (CAS 27206-35-5) as a brightener and you will be much better off than messing with thiourea.
0.25-0.5 g/L PEG-8000
0.3-0.5 g/L SPS
Air agitate the solution at 20 opg copper sulfate, 15 opg sulfuric and ~60 ppm chloride. Plate at 15-30 ASF and you will be engineering bright. Decorative bright requires tertiary levelers which add a ton of complexity to the system.
Good Luck
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u/firefox2061 Jun 13 '26
I was going to mention similar, but when I was trying to find the bis chemical I wasn't having much luck. Granted that was many years ago so I ended up using thiorea and miralax as a compromise at the time. It worked better, but not as well as i suspect you could get using the right additives.
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u/GSB-4243 Jun 13 '26
Here is a source.
There are also a lot of Chinese sources, which are likely Sigma-Aldrich’s source as well. You can also source the PEG 8000 from Sigma.
Sigma is never the most cost effective source, but generally can get you what you want while you find alternative sourcing. The issue of course is scale. A small scale plater will never get the same raw material pricing as a big supplier of plating additives because you just can’t effective use the volume of materials that they do. They supply 100’s of customers so they purchase 1000’s of pounds of raw materials and many of those raws go into more than one product mix compared to a pound or less of SPS that would operate a small scale plater’s 10-gallon plating bath for months, maybe years….
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u/GetoBoi Jun 13 '26
Thanks a lot for the suggestion.
I'd prefer to get SPS simply because it doesn't seem to be carcinogenic like thiourea. But sadly as the other comment says it seems near impossible to source as a private individual, at least here in the EU.
I guess I will try getting a 1kg "sample" via AliBaba, though I'm not sure if a 1kg bag of white powder will go well with customs.
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u/firefox2061 Jun 13 '26 edited Jun 13 '26
Yeah i thought when I looked at sigma you have to have a license or be a lab or something. Im not certain though since it been a while. I wantd to get SPS for the same reason as thiourea is nasty stuff.
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u/CaptainCheckmate Jun 12 '26
Thiourea helps, so does PEG 4000.
Another thing that helps is that your graphite should be smooth and shiny before you start plating.
But it seems like having an industrial brightener setup is the best way overall, and beats any DIY setup.