Discolouration problem after using Evapo-Rust

I have a discolouration problem after using Evapo-Rust on some bright shiny steel parts (see attachment) - they've gone dark gray (almost black) despite having no apparent rust beforehand. I can get rid of some of it with Scotch-Brite and a fibreglass brush, but a lot of the parts are too small (e.g. the brass bolts in the attached picture are 14 BA), and I can't use it on 10 & 12 BA nuts and bolts. Is there any chemical way of of getting it back to the initial bright & shiny, or am I going to have to paint them. The Evapo-Rust was not perfectly fresh, but hadn't been used a great deal.

Bob

Sounds like you have discovered another method of chemical blacking/greying.

Emgee

It is 'cos you left it in too long. Although different steels and cast iron all behave slightly differently. It is just oxide or phosphate I'm not sure which. You should be able to clean it off with a bit of vinegar left over from your Christmas pickled onions/beetroot.

A fibre glass pencil, wire wool a squirt of 3 in 1 and a lot of patience. Some screws in watches are a lot smaller than 14BA and they clean up OK. Sit down with quiet music playing and decent light. Also as Bazyle above says try vinegar

Roy

I have to confess to leaving it in too long, I was going to take it out after supper, but had a touch of 'red-wine amnesia' which meant it stayed in overnight .

The pickling vinegar seems to be to be doing the job, albeit slowly. I'm leaving a test-piece in it overnight, fingers crossed.

I had something similar a few weeks back, I did 2 batches of parts, the first was fine, left for nearly 2 days without problem, there was noticeable sediment in the tub after doing these parts, the second batch had the black staining around the area in contact with the rust sediment so I'm sure this is something to do with your problem.

After using these rust removal products I ran the solution through a fine grade 125 micron paint filter, I think it's necessary to do this after every use to avoid the sediment contamination to the next part you put in there.

Paint filters are cheap and can be used multiple times with water type solutions so it wouldn't hurt to make sure your stuff is clean, I found even the second use without cleaning had a similar effect.

Edited By Pete. on 20/12/2021 00:35:40