If you can't get the whole set, these are the priorities, regardless of what do you paint exactly:
- The most needed: black (Nuln Oil), blue (Drakenhof Nightshade), neutral brown (Agrax Earthshade)
- Often needed: blue-green (Coelia Greenshade), sepia (Seraphim Sepia), red-brown (Reikland Fleshshade), camo-green (Athonia Camoshade), violet (Druchii Violet)
- Rarely needed: red (Carroburg Crimson), yellow (Cassandora Yellow), green (Biel-Tan Green), orange (Fuegan Orange).
Note that there are glossy variants of these shades, like "Agrax Earthshade Gloss". I don't know the reason you might need them. So be vigilant, don't accidentally buy these.
And last precaution. Yes, you can do washing with regular paints, diluting them with medium or just water. But please, don't do this. It won't work well for you. The shades I've mentioned are worth their price. It's better to spend some money on them, than to suffer without them.
MediumYou'll want to dilute your washes quite often. And water isn't great for this. Watered down wash will create
pooling effect — when colored pigment stays on the borders of the pool, and not spreading equally.
That's why there are
mediums — transparent liquids, that reduce opacity without changing the consistency or the flow.
Again, there are mediums in every manufacturer's lines, but Citadel still beats them with
Lahmian Medium: