Will Promarker blender work on copic or finecolor markers ? can they damage each other or something ?
Promarker, Copic & Finecolour markers all use alcohol based ink, therefore the blenders should work interchangeably between the brands without any foreseen problems. Some brands may have a higher/lesser ratio of solvent in their blenders, therefore you may have to apply more blending where necessary.
As you probably know, blenders don't actually blend colours as one would expect. Instead the solvent bleaches ink that has been already applied to the paper and lightens or removes it. If you work lighter colours (which have a higher ratio of solvent) into darker colours, you'll also see this bleaching taking effect. To achieve a nice blend, it's therefore recommended that you build up layers of colour gradually, and blend with a circular motion.
Note: Some brands do have greater or lesser levels of pigment in the coloured markers however this shouldn't effect the blenders.