So, for removing the grey coating, I used 400 grit wet-dry paper, this did it in very little time. Be aware that this will leave scratches, if you don't want these, you will have to re-finish the blade. Mirror polish is difficult to achieve and means that food will stick a lot, so if you can live with a rougher surface, this will be ok.
For thinning: Well I tried rubbing with wet-dry sandpaper to thin in some places where I could not get with the stone, this did work to a degree, but the results were somewhat irregular. What worked well was his method:
[video=youtube;3jsTtnidY3w]https://www.youtube.com/watch?v=3jsTtnidY3w[/video]
[video=youtube;twP_05UEHIM]https://www.youtube.com/watch?v=twP_05UEHIM[/video]
I used a Kai 320-1000 whetstone for this, meaning the 320 part
Now that I know better, I would get a different stone, but the kai stone is ok.
I applied something similar to the sharpie (for Germans: Edding
)-method: I used 1200 grit sandpaper and polished the blade from time to time. This allows me see the scratch-marks and check where I am removing material. This is very important, check again and again where you are scraping off metal.
This is a LOT of work, especially if you're inexperienced. I have put 5-6 hours into this and I am far from being finished. I learned a lot though, and I did take my time, not taking off material too quickly. Rather, I did some thinning, used the knife for a while to see how it behaved, did some more thinning.... The Tadafusa is perfect for that. I am beginning to get a feeling for the knife and the process. Just so you know - the knife will look different, and this only makes sense if you are willing to learn and invest time and effort. Then, it is very rewarding.
By the way, this is how the knife looks now. I only polished it superficially, since it is not finished I won't remove the deep scratch marks, this takes a lot of time. Only makes sense once you're finished thinning.