I use washing up liquid to remove surface tension.. so that the wash goes down into crevices. If it builds up surface tension
Here are my thoughts on that, Avelorn:
Reducing surface tension allows the paint to flow better since it is more likely to wet a dry surface. Thus the paint flows more smoothly surfaces and also into crevices. Dishwashing liquid and flow improver will do this.
Increasing surface tension makes the paint want to clump, like a drop of PVA glue will try to minimise its surface area. What this means for washing is that once paint gets into a crevice, it will
draw more paint in with it, enhancing the wash effect. PVA glue will do this.
So reducing surface tension means that the paint will get in more easily, but increasing the surface tension means that once in, more will go in. Perhaps the quality of surface tension is more appropriately split into gathering and wetting abilities, where the two are not necessarily related. Perhaps this is accurate (if so, it would explain the miracle of floor wax):
PVA glue - increases gathering, reduces wetting
Dishwashing liquid - decreases gathering, increases wetting
Flow improver - decreases gathering, increases wetting
Acrylic floor wax - increases gathering, increases wetting
While this is in accordance with my experiences, I could be speaking out of my arse. It would be really good if someone could speak authoritavely on this.