Restoration Tip: Electrolysis Derusting

[Ralph Volkert]

There is a lot of info in this thread some good some ... not so

I used to work at a chemical plant specialising in Iron salts and worked with the chemists in the lab closely. I also worked for dept of Metallurgy at Queens University and got to pick their brains to for conservation projects!
(I also got access to the art conservation books at their Library)

Here is a link to a very good article outlining the proceedure and science of electrolysys. (http://myweb.tiscali.co.uk/andyspatch/rust.htm#achieved) The author has most of it right.

Notes!

Electrolysis does not replace lost iron on the piece you are restoring! You are are reducing Fe+III back to FE(0). You are not electroplating iron on to the surface.

The sacrificial anode is so named not because that steel is maggicaly deposited on the item being restored but because it is surrounded by hydrogen and oxygen gas. The electric potential of the power supply is what protects your item, and hastens the destruction of the sacrificical anode if it is made of a reactive material like mild steel.

Caution about using alloys and or stainless steel as sacrificial anode... The alloys such as chromium and other materials are released into the solution
These metals are extremely toxic and extreme care should be used when handling. ESPECIALLY if you are reusing the caustic solution. and allowing the waste metals to accumulate. Do not just throw this solution away in your yard or down the drain. Using just mild steel or an inert material will not create a toxic solution. It will remain just water with caustic pH.

Carbon or other inert anodes (Platinum/gold) can be used if you are REALLY worried about consuming the anodes but really, mild steel is cheap and plentifull

Restoration electrolysys should be done at a rate of approx 1mA/square inch of surface area of the material to be restored. As the author of the article mentiones, if higher rates are used you risk blasting off rust from the item and losing iron that will be lost forever and producing a very uneven and porous iron surface that will rust like a S.O.B. if exposed to the elements again! It can also form that rippling and dimpling effect of uneven iron conversion.

Oh yeah if the item you are restoring has been recovered from salt water the salts need to be leached out first before you use electrolysis. I have soaked steel items in the toilet tank for 6 months. LOL That way you dont forget to change the water and getrid of the chlorides that are leached out.

Too much current produces excessive rates of Hydrogen and oxygen gas production. A very dangerous and explosive situation. High current rates also increase the risk of accidently creating a spark!

Only enough caustic material should be added to the water to make it conductive for low current flow. As rust is converted to iron, current will increase. As hydrogen and oxygen gas are produced, the water content will decrease and it will become more caustic and you guessed it...current will increase.

Mention has also been made of rhubarb leaves and oxalic acid as a rust remover. They are basically the same thing. Note oxalic acid is very toxic. That is why your grandma always told you not to eat the rhubarb leaves!

Oxalic acid reduces rust (Fe+III) which is not water soluble to Fe+II which is water soluble. Rusted iron treated this way literally lets you wash the rust away but as the name (rust removal) suggests this removes iron from the item you are restoring.

Electrolysis, conversts rust (which is Fe2o3) back to iron Fe and if no iron has been lost through leaching or mecanical cleaning should be restored back to its original shape if done slowly and in a controlled manner.

There really is nothing magical about the process and a stable, usable restored object can be obtained.

Oh and if the link to the article is removed send me an email and I will forward it to you.

Good Luck!