George Biddell Airy to Faraday   20 April 1862

1862 April 20

My dear Sir

Can you throw any chemical or galvanic light upon the following matter of preservation?

I have lately had several Navy Chronometers returned, principally I believe from service in rather humid tropical climates, injured by rust. On close examination it is found, in all the instances which have lately occurred, (I know not whether antecedently), that the white or clean steel is perfectly untouched, but the blued steel is heavily rusted.

It is a serious evil, because among the “blued steel” is included the balance-spring, the replacement of which is very expensive.

The bluing, I believe, is produced only by heat: I conceive that there is no pigment as in the lacquering of brass.

Now can you give me any theory on this? And can you suggest any way of curing it?

We commonly imagine that, when brass or gunmetal and steel are in contact, it is the steel which suffers by oxidation. But with different acids it is not so. I had some instruments inclosed in a sound oak box, and after some time I found the whole of the brass and gunmetal covered with a yellow oxide or salt, while the steel pins shone out with an almost preternatural brilliancy.

I am, my dear Sir, | Yours very truly | G.B. Airy

Professor Faraday | &c &c &c