Accidental wash that makes recesses white and applied area matt and cloudy.

[Gonzo100100]

Recently I almost run out of my army painter strong tone wash so I added a little bit of tap water to make it last for a day or two longer (I know that if the water is not deionised then after a week or more, mould can appear). Anyway I began to apply that diluted wash to some parts of my figures and the effect was kind of opposite to the intended one. In the recesses where it should be dark, it was white, and whole area became really matt and cloudy. I had to reapply another wash to fix it but this strange cloudy effect is interesting and I can think of some uses for it where it can work well. I believe I’ll have to do some experimentations but maybe someone just know what is the cause of that effect? Is it high ratio of glycerine, or soap in a paint?

[Vanth]

Might be calcium in the water: if the water in your area is especially hard, it might happen. One of the reasons why it is a goo thing to use demineralized water for painting.

[vexillia]

All washes are pigment suspended in an acrylic medium.  The medium is a mixture of acrylic resin and a surfactant. Adding water to the dog end of a bottle will significantly dilute the medium ending it's ability to suspend the pigment and the acrylic polymer in the medium itself.  To heavily dilute a wash you should add more medium as well as water.

P.S. Glycerine and soap are seldom used in modern paints.

[Daeothar]

Older Vallejo washes had exactly the same issue.

Solution; do not dilute with water but with medium and you're good to go... 

[Major_Gilbear]

Most washes are designed to dry matte, therefore they usually contain matting agent.

As Vexilla says, this is suspended in an an acrylic medium with the other components of the wash. By over-thinning with water, the medium starts to break down, and this reduces it's capacity to hold the matting agent. The white soapy marks you see are the dried remains of the matting agent where is has over-accumulated having failed to remain suspended in the medium to give the intended even (and therefore see-through) effect to the model.

Adding more medium as well as a little water fixes this.

By the way, you can also get similar effects with paint if you over-thin it. Done deliberately, it can produce interesting effects, like this model's sword (painted by another LAF member here):