It's really annoying me, but I saw a decent tutorial on exactly this subject just a week or so ago - and now I can't find it!
Anyway, there are two kinds of Decal paper, and two useful colours too.
1) Decal paper is for Laser printers
or for Inkjet printers - make sure you have the right one!
2) For each printer type, there are two main colours - White and Clear. Negative spaces (those that are not printed upon) are where the decal you have chosen will be visible. So if you want to do white tactical markings on an Ultramarine for example, you will have to use the white paper and do an outline.
3) Once you've printed your decals (run some test copies on normal paper first for scaling and design checks), let them dry fully.
4) Using a
gloss spray, spray the decal sheets thoroughly and evenly. Let this dry too. You may want to spray a second time and then let it dry again. The gloss spray (and it must be gloss!) seals the printer ink against the decal paper.
5) Carefully cut out your decals with a very sharp razor and apply as normal to your model. Check out Micro Sol and Micro Set if you don't already use them.
6) You can seal your model as normal at the end with a matte finish.
/// Edit: Found it!
Linky. ///
