Rust blueing is a multiple step process that involves
1. cleaning and preparing the surface to be rusted. This would include polishing the metal to the desired finish level
2. Applying the rusting agent. Normally a mix of nitric and chloride salts and agents to produce the rusting. The faster acting the agent the coarser the rust and resulting finish
3. Rusting the part. Rusting can be done in air but it production environments some manner of steam cabinet id generally used. The hotter the temperature, and the higher the humidity the faster rusting process with the same comments as in 2.
4. After the rusting the part is Boiled or steamed to convert the red oxide to a darker black oxide.
5. The loose rust is "carded off" to leave the darker iron oxide on the metal. Carding almost always is done with a very fine wire wheel or wire brush. "Carding" is used in the sense that it is in wool or linen manufacuturing
6. Back to step two and repeat until the desired color is reached..
The carding step would be very difficult on interior machined surfaces. It can be done but it it awkward trying to get the loose rust off.
PS, I agree that the P08 may have been mounted on various jigs for this process. But I doubt there was a single wooden jig in the whole DWM factory.
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