A few months ago I bought some Acrylic Flow Improver by Winsor & Newton. This was the first time I'd bought a product like this. Previously I had used washing up liquid (!) to break the surface tension of washes. The obvious problem with that method was the tendency for the resulting mix to be soapy and frothy. Needless to say this was not good for smooth finishes. Often I would find 'tide' marks where washes had pooled in recesses or mottled surfaces where bubbles had formed. More than one model need to be reworked to correct problems with my technique.
I had read about flow improver's but hadn't really understood their capabilities. Then last summer I found another article about flow improver and felt it was time to make a leap of faith and try one out. I opted for Winsor & Newton simply because I trust the brand.
To use simply mix a ratio of water and flow improver. The resultant water mix can be used to dilute paints either for blending or creating washes and glazes. Again I fell back on various literature for instructions on what ratio of flow improver and water to use. Unfortunately there didn't seem to be any clear guidance so I decided to experiment and work it out for myself.
I won't bore you with the details of my experiments but what I eventually settled on was the following. Mix 20% Flow Improver with 80% Water (Ratio of 1:4). I made up a dropper bottle with about 16ml in it for ease of use. For layering I use 4 parts water to one part paint. For washes the ratio is 10 parts water to one part paint. Theses are rough guidelines as the consistency of paints can vary and exact dilution needs to be determined at the time of use.
When creating washes I find it best to create a mixture that looks a little like water paint. One tip I picked up was to use a bit of wash on newsprint. If you can just see the text beneath the wash then the consistency is correct.