Garnet Paper and Natural Japanese Sharpening Stones.
We did use to use an abrasive called garnet papers when sanding components. These were nice pale brown sheets of abrasive with what was called open coat abrasive. That was a gap between the particles of abrasive showing on the backing sheet. The good thing about open coat was that it gave a place for the dust to go. We now have aluminium oxide papers with a closed coat that is really designed for machine sanding. Not so good and garnet is now not so easy to find.
The great feature that I want to suggest to you was the way the garnet abrasive wore down . Aluminium oxide stays pretty sharp for ages then it dulls. Not much abrasion takes place as it gets dull. Garnet didn’t seem to do this, granet would fracture leaving a new sharp edge. The paper seemed to sand at a finer level and still be sharp. So a 180 grit garnet would also cut at 220 if you used it correctly. It did however break down pretty quickly and was useless for machine sanding.
This has been brought to mind by my search for a natural sharpening stone from Japan. I am just in the process of buying a new stone and I am reminded of this quality that natural abrasives have as they break down to a finer cut as you use them . As one polishes a blade the practice is to rub a little less hard build up a slurry under the blade and let that work away at removing the fine scratches.
The current thought is that man made stones like King are great but they cut a v shaped scratch in the steel, natural abrasives cut u shaped scratch so helping to remove the marks of the man made stone . We use King 12000 as our final polish and I am seeking to improve on that a bit. We will see…..
I am looking at a Ohirayama Renge Suita that is being recommended to me by Tomohito-san . I have been buying plane bodies and blades from this small supplier for some time now . He has always advised me well and i have come to trust his advice. When buying from the other side of the world from a country with a different culture to ones own it is best to seek guidance.