oak shard
For something to look on fire you need to go very bright. You can go white or almost white, but that yellow is much too dark for your brightest light.
Do you have a reference for the sort of look you’re going for?
That will both make it easier for you to decide how to paint it and to give advice on how to proceed.
oak shard
Alright, so analysing your references and your paint job we learn that your value range is nowhere near what you’re targeting.
You need to go much brighter, almost to a white, in your lit areas. And you can go almost full black in the coldest parts, furthest from the heat source.
Notice how a light from within is exactly opposite to how we usually paint light on minis. Your recesses should be the brightest. In the artwork the figures even have white mouths.
No, you don’t have to base white. It makes it easier with something like this, but not needed.
White ink or thinned down white paint can be helpful to get those recesses painted.
I will say though, for all their years of experience, Games Workshop have not managed to produce a useable white paint, so don’t get frustrated if this is difficult.
You start with the white and go progressively darker usually, but it doesn’t really matter as long as you end up with a gradient from white to very dark red.
I don’t know what this means.
Are you asking if you should put a wash over the whole thing in the end?
If so no, definitely not.
The purpose of a wash is to darken the recesses, you want the opposite effect.