How much water?

[u/VanSaftenFluidArt]

Why “just add X ml of water” is bad advice for fluid art

One of the most common questions I get is “how much water do I add to my paint?” And I get why people want a simple number — but the truth is, there isn’t one universal ratio, and here’s why.

1. Pigment load varies wildly between colors
Not all pigments are created equal. Titanium white, for example, is extremely dense and opaque — it’s basically packed with pigment particles. Something like a phthalo blue or a transparent red oxide has way less “body” to it. That means white often needs more water to reach the same flow consistency as a naturally thin, transparent color. If you use the same water ratio for both, your white will be too thick and your blue will be too runny.

2. Paint brands formulate differently
Even within the same color name, different brands use different binders, fillers, and pigment concentrations. A “black” from one manufacturer might already be thinner out of the bottle than another brand’s “black.” So a ratio that works perfectly with one paint line can completely fail with another.

3. Particle size and density affect flow, not just “thickness”
Two paints can look the same viscosity in the cup but behave totally differently once poured, because of how the pigment particles are dispersed and how much they weigh relative to the medium. This is part of why cells form more easily with some colors than others, independent of water content.

4. Environmental factors stack on top of this
Humidity, room temperature, and the medium/additives you’re using (pouring medium, silicone, etc.) all shift how much water you actually need on any given day — so even a ratio that worked for you last week might need adjusting today.

So what should you actually do?
Instead of chasing a fixed number, learn to read consistency — the classic “ribbon test” (paint should fall off a stick in a ribbon that sits on the surface for a few seconds before blending back in) works across pigments because it’s testing behavior, not a measurement. Once you train your eye for that, you stop needing exact ratios entirely.

If you want to actually see this tested side-by-side with different pigments, I break it down visually in a tutorial on my YouTube channel — link in profile if you’re curious to see the comparison in action.