Hi Darren
I have spent years trying out different acrylics and mediums. My aim was to try and find an acrylic which when dry did not loose too much of its film thickness and did not dry so quickly.
Here are my findings
Acrylics:
If you paint in glazes than the new “artists acrylic “ from winsor and Newton are the best as they are made with a new clear polymer which has no cloudiness when wet and dries with no colour shift
If you paint with thicker paint then I would recommend the ultra thick acrylics from liquitex, these are the thickest acrylics I have tried,( too thick for some people) have little shrinkage and colour shift from wet to dry they are very economical compared to winsor and newton
Mediums:
I haven’t tried the new winsor and Newton mediums yet but I can recommend the liquitex mediums and gels. There slow dry glazing medium is very good almost clear when wet and dries clear. if you like thicker paint then slow dry gel or ultra thick gels are also good. If you glaze then I would try the winsor and Newton glazing medium but as I say I have not tried it.
Liquitex do a product called liquithick which thickens up acrylics and makes feel more oil like. You only need to add very little 10% but no more than 25% I love the stuff
For many years I used a stay wet palette for mixing paints on. It is basically a sheet of blotting paper on which you place a permeable membrane. If you use this method then thoroughly wet both the blotting paper and membrane and then blot most of the water from it so it is just damp or the paint will reduced to liquid acrylic over night. After a couple of days it will start to dry so regularly spray with water by lifting up the membrane and spraying the blotting paper. If you close the lid when you take a break the paint can be kept wet indefinitely.
As I paint thicker and mix large mounds of paint I now tend to use a piece of Perspex and spray it with a spray diffuser mixed with 20% acrylic retarder.
I read somewhere that an unglazed and unsealed ceramic tile can be wet and then used as a palette to keep the paint wet but I have still to try this.
If you use acrylic primed canvas / canvas board I sometimes thoroughly wet this before paint application. Acrylic gesso absorbs water (until the first layer of acrylic has dried) this keeps the first application wet for longer
I often spay the wet acrylic on the canvas with water or my water retarder mixture every couple of minutes, (don’t over spray though) this can keep the paint wet for ages, good for blending
Hope this helps
Paul M
http://www.paulmilner.co.uk/