Dulling the shine on a stainless steel ball

I am about to finish a model that has a governor using two 5/16" diameter stainless steel balls as bob weights. These are highly polished and far brighter than the rest of the steel work. I want to reduce their shine without using paint or damaging them (each has a tapped 10BA hole for the governor arms).

At the moment I am seeing if citric acid (the strongest acid I have and am prepared to use) will etch the surface (using a spare ball). However this does not seem promising.

Does anyone have any ideas?

JA

Scotchbrite if you want a matt finish. Steel wool and oil if you want a dull lustre. Spin the balls at high rpm and apply.

As Hopper says Scotchbrite pad will give a brushed look

Most stainless steels are resistant to most acids. A possible attack may be initiated by releasing Chlorine, from bleach, with acid. Not sure if it occurs with citric acid, but you have absolutely no chance of attacking any decent S/S with citric on its own. Think here of kitchen saucepans?

Chlorine is a very nasty substance and any production is not recommended (for the vast majority of the population).🙂

I am confident that grit blasting would knock the shine off them.

We never subjected stainless steel to hydrochloric acid - we always used glass-coated vessels - but nitric (on its own) was often used to dissolve lesser noble metals than gold and platinum, and base metals, in stainless steel vessels. Aqua regia was required for dissolution of gold and platinum (but Chlorine bubbled through hot conc. Hydrochloric acid was/is the preferred method for dissolving gold and platinum, in the precious metals industry).

If you have a slow running motor you could try tumbling them with an abrasive. Or try electrolysis in brine, but be careful as Chlorine and Hydrogen will be released.

Another vote for mechanical abrasion. Not easy to attack an alloy intended to resist corrosion with a chemical. Doubly so if you don't know exactly what the alloy is - some are formulated to resist acids, others chlorides. The balls might not even be stainless steel. Could be a chrome plate or other finish on an ordinary core.

NDIY's already covered Chlorine, Acids and mixtures that might work. They're all off-the-scale aggressive potions compared with Citric Acid.

Many Stainless Steels and bearing platings are also too hard for mild abrasives. So I'd try gently rubbing the governor balls zig-zag with a coarse Emery paper or scotcbrite whilst they spin slowly in a lathe. (Emery paper on a lolly-stick or similar to keep fingers safe.)

Dave

Fine valve grinding paste?

Slow speed is no good for a decent uniform finish with a scotchbrite pad, I've always brush finished stainless at high speed as earlier mehtioned.

I dripped a spot of Harpic 100% Limescale remover on a stainless steel knife. Next day there was a neat matt finished mark. It even says on the container not to use it on stainless steel.

Try dropping your balls in some of that.

This might sting a little.

It will certainly take the lustre off your cluster!

Harpic limescale remover is hydrochloric acid, which attacks stainless. I think brick acid is as well. When I was a teenager, Boots would sell you a bottle of conc hydrochloric, no more I suspect

Harpic limescale remover is hydrochloric acid, which attacks stainless. I think brick acid is as well. When I was a teenager, Boots would sell you a bottle of conc hydrochloric, no more I suspect

Sounds like just the job for a Rock Tumbler if you can beg/borrow/find-before-it's-lost one.

Not worth buying one for this one task though.

I bead blasted mine with a fine glass bead.

Phil

Use Scotchbrite by all means, but you don't need to revolve the balls. just add a few drops of oil to a fine Scotchbrite sheet and massage each ball for about the same period. This will take the gloss off in a way that should show no particular direction in the texture.

By Scotchbrite I mean the plastic mesh stuff like posh pan scourers, in which fine abrasive is embedded - available from eg Axminster whose customers use it to dull the gloss on varnish etc.

Cheers, Tim

The effect of Hydrochloric acid is likely to depend on the grade of stainless used. There are 'marine' grades used for yatch chandlery which are much more resistant to sea water corrosion. And the main problem in sea water is the chloride content.

And PS - we learn above that chlorine bubbled through HCl is used instead of aqua regia to attack gold. Could this possibly have been a mis-remembering and the conc acid involved was nitiric. perhaps?

Regards, Tim

I stand corrected. I've only tried this once, not with a pad, and high-speed created an awkward to remove band. If Bezzer's done it more than once I believe him!

Mirka do good quality scotchbrite pads, maroon is very fine Al Ox, grey is ultra fine Sil carbide which should work well dulling stainless.

Yes, you are either mis-remembering or never completely knew. Aqua Regia is typically 2/3rds hydrochloric and 1/3rd nitric. The nitric is required as an oxidising agent.

To dissolve precious metals, one requires an oxidising acidic environment. Hydrochoric/Nitric acid mixture historically provided a suitable mixture for dissolving gold.

However, to recover all of the gold, one needs to remove all of the nitrates in order to recover the gold quantitatively. The adoption of using Chlorine as the oxidising agent avoids the introduction of nitrates, which, if any is left in the solutions it prevents the last small losses in the effluent.

Nascent hydrogen was ineffective in completely destroying the residual nitrates in solution, thereby leaving a small amount of gold in solution after reducing with sulphite. We were recovering trace amounts from multiple cubic meters of effluent, before it was dumped down the drain - a bit different to laboratory beaker experiments!