Thread: Rust removal with Citric Acid - pictorial step by step

Hi Paul, there are many fans of Electrolysis on the forum, although i have never tried it myself. Apparently there is some risk involved, but others would know better than I.

AFAIK, the big advantage is that when there is no more rust the process stops, and therefore doesn't do any pitting damage, which can occur with acid.

Hello Fence Furniture,

Excellent article. Will give it a go over the electrolysis. I have a couple of old handsaws to clean-up. Thanks, John M.

I might give it a go and compare it with the electrolysis method. I got two very old and rusty planes that I'd like to do rehab.

Originally Posted by FenceFurniture

AFAIK, the big advantage is that when there is no more rust the process stops, and therefore doesn't do any pitting damage, which can occur with Electrolysis.

This is not correct. Pitting only occurs with electrolysis if the object being derusted is connected to the wrong terminal. In contrast, using acids, will eventually pit the metal surface if the object is left in the acid long enough. The advantage of citric acid is that like acetic it is a weak acid so pitting will happen slowly.

Originally Posted by BobL

This is not correct. Pitting only occurs with electrolysis if the object being derusted is connected to the wrong terminal. In contrast, using acids, will eventually pit the metal surface if the object is left in the acid long enough. The advantage of citric acid is that like acetic it is a weak acid so pitting will happen slowly.

It sure is wrong Bob, I've just changed "Electrolysis" to "acid" in that post. Oopsie!

Thank you all for the information and tutorial working with rust and citric acid.
Dissociated in water, iron citrate is quite soluble and should washe away.

According to what I read in Leonard Lee's book, the rust pitting happens long before you got the tool to attempt rehab.
I am not about to try to grind a tool edge back through one old rust pit after another, even if they are cleaner than my kids ears after a bath.
I won't soak a tool in citric acid for 6 weeks so further pitting won't be any consideration.

I am hoping to find one or more draw knives and spoke shaves for a particular wood carving project. I fully expect to want/desire to clean them up a little but functionality is paramount.

I built a simple coat rack from railroad spikes and an oak 2x4. The spikes had been in the lake since about 1912. Let's talk rust clean-up.

Test post (to see if i can reply now)

I just tried the citric acid on some triton and P&N drill bits which had some rust on them

marvellous - will now go looking for other rusty stuff

Originally Posted by Sawdust Maker

I just tried the citric acid on some triton and P&N drill bits which had some rust on them

marvellous - will now go looking for other rusty stuff

Yeah, good eh? Did you get it at the supermarket?

raided the spices cabinet but more-n-likely from supermarket originlly

I put these old router bits into citric acid over night and received my usual good result.
IMG_0132.jpg

The thing is, when I took the lid off the tub I usually use for this, I found an old bolt that I had put in over a month ago maybe closer to 2 months, and forgotten about.

The bolt was covered in black in slime but after the rotary wire brush came up bright as a button.
IMG_0131.jpg

It seems to me that once the rust is "deactivated"? the citric acid stops working. Or maybe the citric acid looses its potency (all non scientific terms). You can see the pitting on the bolt but I suspect that the rust caused this.

I find that electrolysis is very useful for the big stuff and safe in a ventilated garage. All you need is a tub of water and a handful of some sort of soda crystal.

TT

Originally Posted by Twisted Tenon

The bolt was covered in black in slime but after the rotary wire brush came up bright as a button.
IMG_0131.jpg

It seems to me that once the rust is "deactivated"? the citric acid stops working. Or maybe the citric acid looses its potency (all non scientific terms). You can see the pitting on the bolt but I suspect that the rust caused this.

Two things TT:

• If you used the same batch of acid then it couldn't have been deactivated - it worked on the router blades. Whether or not the pitting is caused by rust or acid, or a bit of both, is unkown. Heavansabove maintains that CA will not pit cast iron, but will pit steel.
• That black slime is actually a mild rust inhibitor. For things that I don't need shiny I just scrub with a plastic brush under running water. The black goes and leaves a paler grey residue, which may be pearlite, and is less prone to rust than bare steel.

Good result though eh?

Originally Posted by FenceFurniture

Two things TT:

• If you used the same batch of acid then it couldn't have been deactivated - it worked on the router blades. Whether or not the pitting is caused by rust or acid, or a bit of both, is unkown. Heavansabove maintains that CA will not pit cast iron, but will pit steel.
• That black slime is actually a mild rust inhibitor. For things that I don't need shiny I just scrub with a plastic brush under running water. The black goes and leaves a paler grey residue, which may be pearlite, and is less prone to rust than bare steel.

Good result though eh?

It was a fresh batch FF. I should have explained that better. The bit about an inhibiter makes sense. What I like about citric acid and electrolysis is that all you need is water and the respective crystals.
TT

As an experiment, put some steel (plastic does not work) tent pegs out in the rain for a while until all are covered in a film of rust.

Then make up some citric acid solution and put in the tent pegs. After one hour take one out and scrub the deposit off - it will be rust free, and no pitting. Take out another one after overnight soaking and you will need to work hard to get rid of tiny pitting. Leave for 2 days and take out another one - this will be obviously pitted after removal of the deposit and grey (not shiny). Take out another one after a week and there will be severe pitting.

The Message

Do not leave in overnight, but use strong and hot solution - and check regularly - AND remove as soon as the rust has gone from the surface, ie you need to remove the gunk with a stiff brush and examine progress. If the metal is already rust pitted, then that is unfortunate but you can not get rid of those pits with citric acid.

Cheers
Peter