Originally Posted by
hatzicho
Well colors of the ready to use pastes you can buy are vacant these days. The incredients differ from producer to producer, there are green pastes that are much coarser than the normal chromium oxide and so on.
I never use ready to use pastes, I produce all pastes that I use by myself, based on old receptures from grinders and my own experience. You can buy nearly all grinding and polishing powders as pigment.
So chromium oxide green is nearly all the same concerning the average or maximum particle size, that is around 0.3 µm. Concerning the red iron oxid Fe2O3 you can get variable particle sizes between 0.07 µm - which is much finer than chromium oxide - and > 1 µm.
You are correct that the ancient Sheffield polish was a mixture of several iron oxides that was mined as a natural product. It was developped around 1700 by the swedish engineer Christopher Polhem. The Solingen grinder Daniel Peres did a lot of efforts and years of experiments to recreate this polish by mixture of different iron oxides beginning of the 19th century.
Indeed the particles of red iron oxide are not as stable as chromium oxide particles. But that is also part of the trick, the particles getting smaller during polishing and therefore create a more mirror polishing. The problem is, that the surfaces must be very well prepared and nearly already without deeper scratches to use iron oxide. Otherwise you simply polish the scratches - which makes them even more visible on the surface.
As for the time you need for ploshing that is hard to say. If the surface is well prepared you can do the job quite quickly. But it is necessary that the metall surface heats up, therefore a certain pressure is needed. But I found that polishing with iron oxide you don't need so much pressure and time as when you polish with chromium oxide.
Regards Peter