I'm not so worried about my Scottish/GB stock, that's easily obtained if I go really wrong and most wasn't that expensive, it's my much more expensive CIE stock I'm worried about(!).It's not hard at all. I use watercolours as used for art, plenty of water then wipe off after 5 seconds. It works and details get kept in indentures more than on the flat body. Rough/porous surfaces are best though.