Let me say you make a straight razor - or any other not so usual shape of a blade. Take anytype of non-flat grind be it a simple Concave (hollow) ground blade or some complicate multi-fullered blade. As soon as it comes to finishing & polishing you will need a matching sanding block. Something wich has the right hardness, the perfectly matching profile.

And to top it all off - it should be easy and quick to make, something you will not spend hours on making.

If you just work a few different shapes, you could go and hand-profile a selected number of tools and be done with it - however as soon as you require a lot of different shapes you're usually out of luck.

Well - not really... my old time "use-and-abuse-it-for-all-thing" "FIMO" (Plastiline) can work wonders here...

What I do is that I take half a block of FIMO and press it onto a piece of scrap wood - mould the edges around the wood so that it sticks to the wood easily.

Then I press the wood-backed fimo thing onto the slightly oiled (this is important or the fimo will stick to the steel) blade.

The Plastiline-stuff will perfectly mould to accomodate the most complex shape ... when I am satisfied with the pressed FIMO I put it in my kitchen-oven at 110°C for around 30 minuts and then let it cool down.

Photos:

FIMO Block in black (ordinary hardening plastiline)