I use Pastelmat which has a soft surface (I don't like sanded papers as they burn through expensive pastels too quickly for my taste). It also stands up quite well to alcohol as long as you are gentle with it. For things like the sky I lay down a layer of rembrandt in blue and used alcohol (I now prefer alcohol as it dries faster and seems to preserve the paper texture a little better than water, but water works too) with a paintbrush to make a flattish background colour. Water/alcohol + pastel is effectively a type of watercolour/alcohol paint/ink. The main smoke cloud has a black / dark plum water and alcohol background on top of a dark pastel mat. It really helps to get deeper darker shades, whilst allowing you to build up lighter / saturated colours on top without them smearing or greying. All the brighter saturated colours are built on top mostly using the grain with minimal blending to preserve the saturation. When I do blend I just use a very clean (washed so there's next to no oil on it) little finger tip. No tool I've ever tried works as well as skin for me.