Welcome to Gaia! ::

erm... it depends on how you want the "molten" rock to look. and the type of rock you want it to be.

if your going for the generic blackened rock floating in magma, then paint the rock in one consisted colour 1st. then paint the magma in a gradient, with the darkest colour closest to the rock, and up to a creamy white at the edge of the base. you could then drybrush the light effects onto the rock

if you want the rock itself to physically be magma, then i wouldn't know what to suggest, although a cool idea would be to paint thin lines of magma on the rock (as if tiny streams of magma are escaping from inside it, or being created on the rock by the heat of the dragon) that effect could be achieved with 2 colours, a light red and a creamy white, start by painting the lines in the red, then do a thinner line down the middle of the white.

alright, ive got a better explaination, and a more... "specific" question.

firstoff, heres the "model" im painting (so far its just got an undercoat of scab red on it)

full shot so you know what it looks like
rock1
rock2

ok, so, in the cracks of it, im trying for thin cracks, like the cooling top layer of a puddle of lava cracking, and showing the lava underneath

i found a picture on GW's site, but it seems to be down for the time being, so the next best picture i know of is one of DE's
(Stolen, please forgive me)
the problem seems to be is that, unlike my rock, this example is flat, thus, it seems more... "easy" to do...
my question(s) now being. how can i paint on that lava, then paint on black, leaving a thin line of lava?
drybrushing would leave; 1. brushed, unsolid lines, and 2. streaks of lava way too wide.
does anyone know of any painting techniques that i could do to make a nice, solid, natural line where the lava underneath the rock, and the rock, meet?

I guess a good question to ask is where EXACTLY do you want the lava? I mean, a practical one if you are looking for lines is in the concave corners of the rock, in which case I would say just paint a thicker line of like orange or red then gradient it into bright yellow or white in the middle.

Another useful piece of info would be, do you want it too look like lava would be flowing down the rock or like the cracks in the rock are red hot?

Perhaps it would be easier to get the red hot painted first, so like make a heavy white undercoat at least in the cracks that you want and then just kinda fade to like an orange then to a cool red, and then paint the rest of the rock just without painting the cracks.

This is just an idea, ive never actually tried something like this before, but it sounds like a really cool idea. The above is just what I THINK would work, and I by no means guarantee that it would work.

I agree with the white undercoat idea; it makes it stand out as brighter, just be careful with it and make sure you get it evenly layered down to the color you want, blended slightly so it's not quite all the same color.

You want white as the -bottom- coat. Apply gradually darker colors (yellow, then orange) on top of it with a technique similar to dry-brushing, except with much -less- paint, so that the layering comes out evenly, smoothly. That way, when you're done, you'll have some spots that are darker and some that are lighter, but they blend together well in appearance, without visible paintstrokes.

http://www.heresy-online.net/forums/showthread.php?t=6410

Step-by-step guide for lava bases.