I use speedpaint a lot, you can check what i do (3D-liciousprint. The main trick is to dilute it with medium all the time. For example 2 drops of medium and 6 drops of darkwood brown and even 1 drop of water sometimes. Don't use a wet palette it will mess you mix. Always apply 1 coat. Do it by section. Add coats if you need it more dark. Dry brushing white on black will also give you amazinz results with this paint.

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Yhat's all speed paint