Different physical properties of alcohol and water molecules lead to the effects of techniques.
by Bruno Weiss
My name is Bruno, I'm graduated in Molecular Biology and I'm a watercolorist too. I'm here just to point a little mistake that I have read at the paragraph "Alcohol Textures Watercolor Techniques" find in this site. You have said that alcohol and water don't mix. Actually they mix (and mix really very well). I believe you have mistaken alcohol and oil (oil doesn't mix with water).
The effect obtained with alcohol on the watercolor is due to other properties of the molecules of water and alcohol. Alcohol dilutes the pigments of the paint much better than does water (that's why when you spread alcohol before covering the paper with water-dilluted paint the result is usually darker stains - the alcohol "holds" harder the majority of the paints molecules and the underlying paper, than does water).
Other effect is that the alcohol runs faster between the fibers of the paper than does water. So, when you spread alcohol over a wet water-dilluted paint, the alcohol leaves that "foam" effect - the alcohol dilutes better the paint than water (so it acts sort of a 'magnet' for the paint, taking it off from the 'influence' of the water molecules, re-diluting it) and then runs over the water, diluting itself and leaving the paint that it had bring together behind as it dilutes in the water that was already on the paper's fibres.
Thanks for your time,