Watercolor Mixing Chart Builder

How to use the Watercolor Mixing Chart Builder

1. Pick the paints you own. Search by name or by pigment code (type PB29 or “ultramarine”), or narrow the list with the color-family chips, then press a pigment to add it. The starter set is a six-paint palette: one yellow, a warm and a cool red, a warm and a cool blue, and Burnt Sienna. Up to 16 paints fit on one chart.
2. Add anything that isn’t listed. Under Add a custom paint, type its name, set its color with the swatch and press Add. Use the ↑ buttons to reorder your list — grouping paints by hue makes the finished chart much easier to read.
3. Choose the look. Simulated mixes predicts every pairing. Wash draws each cell from full strength down to a pale glaze, the way a painted swatch looks; Flat shows one color per cell. Half grid drops the mirror-image cells above the diagonal, and Tint row adds a diluted strip of each paint underneath.
4. Read any mix. Click a cell, or tab to the chart and use the arrow keys. The panel below names the two paints and gives an approximate HEX value you can copy.
5. Print the real chart. Switch to Blank template, pick Letter or A4 and press Download PDF. You get a grid labeled with your paint names and color chips, with blanks for brand, paper and date. Download PNG saves whichever version is on screen. Your list is remembered in this browser, and the page link carries it too.

Why painters still make mixing charts

A palette is only the starting point; most of the color in a finished painting is mixed. Six paints give you 15 distinct two-paint mixes. Twelve give 66, and sixteen give 120. Nobody holds that many results in their head, which is why a mixing chart is the first thing many teachers ask students to paint: it turns a box of tubes into a map of what the box can actually do. You find out which pair makes a clean violet, which makes a granulating gray, and which yellow turns muddy next to which blue.

Paint also refuses to behave like screen color. A monitor adds light, so averaging two RGB values is a fair guess for mixing light. Pigments subtract: each one absorbs part of the spectrum, and a mix absorbs roughly what both absorb. Average the RGB values of Hansa Yellow #F6C51C and French Ultramarine #27389C and you get #8F7F5C, a khaki gray. On paper the same pair gives a soft olive green, because both pigments happen to reflect some green light and nothing else survives.

Labels mislead too. “Sap Green” from one brand and “Sap Green” from another can share no pigments at all, while Burnt Sienna and Raw Umber are often both PBr7, natural iron oxide. That is why every paint in the list carries its Colour Index code. When you chart by code, the chart stays useful even after you switch brands.

How the simulation works, and where it breaks

The model follows Kubelka–Munk theory, the standard physics of paint films. At each wavelength a pigment layer has an absorption-to-scattering ratio, K/S, computed from its reflectance R as K/S = (1 − R)² / 2R. Mixing averages K/S, not color.

A quick worked example at one wavelength of green light: an ultramarine film that reflects 5% has K/S = 9.03, and a yellow that reflects 70% has K/S = 0.064. An equal mix averages to 4.54, which converts back to about 9% reflectance. A plain average of the two reflectances would predict 37.5%, four times brighter. That gap is why naive digital mixing looks chalky next to real paint.

The tool fits a smooth reflectance curve, sampled at 36 points from 380 to 730 nm, to each paint’s swatch color, mixes K/S band by band and converts the result back to screen color. Each paint’s share is weighted by its lightness, so a dark, strong paint like Phthalo Blue goes in at a smaller dose, which is what you do at the palette when you aim for a balanced middle mix. The model can’t know:

• Granulation. French Ultramarine (PB29), Cobalt Blue (PB28) and Cerulean (PB35) settle into the paper’s tooth and give textured mixes; the screen shows them smooth.
• Opacity. Cerulean and Chromium Oxide Green (PG17) mix chalkier than their swatches suggest.
• The real spectrum. Two paints that look identical in the tube can absorb differently and mix differently. The model only sees one color per paint.
• Whites. Chinese White and Titanium White lighten real mixes more strongly than this single-ratio model predicts.

Mixes worth painting first

Compare the two green rows in the simulation: the only change is the blue, yet one green is vivid and the other is muted. If you want to check how long any of these pigments will last on a wall, look them up in the Pigment Lightfastness Lookup.

Tips from practice

Paint the chart on the paper you really use. Cotton paper and cellulose student paper take the same mix differently, so a chart on printer paper tells you little. Use the PDF as a layout guide: tape it beside your sheet or put it on a light box and rule the grid in pencil.

Work in a checkerboard. Paint alternate cells first and fill in the rest once they are bone dry. Wet neighbors bleed into each other, and a bled cell shows neither mix honestly.

Grade every cell from strong to pale. Start the top of the cell at full strength and add water as you pull down. The top shows the masstone, the bottom shows how the mix behaves as a glaze; the Wash cell style imitates exactly that.

Bring strong stainers in by the drop. Phthalos and quinacridones overpower almost everything. Put the weaker paint on the palette first and touch the strong one in with the tip of the brush until the mix sits halfway.

Write the brand and date on the chart. Manufacturers reformulate, and a chart from five years ago may not match a fresh tube. When a mix surprises you, the Paint Mixing Calculator is a quick way to look for a closer pair.