Free Glaze Layer Simulator
Glazing is painting with coloured light: a thin film that deepens and hues whatever lies beneath without hiding it. Stack up to four layers of any of 22 pigments over your photo or underpainting, each glazed as a clear film or scumbled on as a broken, dry-brushed one. Every layer is computed with Kubelka–Munk over the colour beneath it, and a pen's pressure sets how strongly your brush lays each layer where you paint it. Exports PNG. Free, with no sign-up, and your picture never leaves your device.
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The whole stack over three grounds
- over white
- over mid grey
- over dark
Left third: the bare ground. The same glaze glows over white and nearly vanishes over a dark. Films are computed with Kubelka–Munk from each paint's masstone colour; real glazes also depend on pigment load, medium and brand, so test on a corner of the painting.
Layered glazes.Up to 4 layers, each with its own pigment, film thickness and order; each is computed over everything beneath it.
Scumble mode.A broken, dry-brushed film with a coverage slider: light opaque paint veils a dark passage between streaks of the layer below.
Pressure-sensitive brush.Paint where a layer goes; with a pen, pressure sets how strongly each dab applies. Erase and clear per layer.
The stack over three grounds.Swatches of the whole stack over white, mid grey and a dark, beside each bare ground.
- Free
- No sign-up
- Runs in your browser: your image never leaves your device
What is glazing in painting?
Glazing is painting a thin, transparent layer of colour over a dry layer, so the paint below shows through, darkened and tinted by the film. This simulator previews it on a photo: stack up to four glazes or scumbles of 22 pigments, each computed with Kubelka–Munk over the colour beneath it.
How to use the Glaze Layer Simulator
The tool takes 6 steps, all on your device.
Drop in a photo of your underpainting, or send a study from the Underpainting Generator with Glaze over it.
Layer 1 starts as an Alizarin Crimson glaze. Change its Pigment and Film thickness; the preview updates as you drag.
Press Add a layer for a second film on top. Choose Glaze for a continuous transparent film, or Scumble for a broken one, and set its Coverage.
To keep a layer to one passage, turn on Only where I paint and brush it onto the picture; with a pen, press harder for a stronger layer. Erase or clear the mask as needed.
Reorder layers with the arrows: the first layer goes on first, and order changes the result.
Export PNG to keep the plan beside the easel.
What the Glaze Layer Simulator does
The Glaze Layer Simulator lays Kubelka–Munk films over an underlayer you load, fast enough to drag, and exports at full size.
Kubelka–Munk films
Each layer uses Kubelka–Munk's reflectance for a film of finite thickness over a background, band by band across a 38-band reflectance curve from spectral.js. A thin film tends to the colour below, a thick one to the paint's masstone. Among the value and tone tools for artists, it is the one for planning layers.
The underlayer matters
Because each film is computed over the actual colour beneath it, a glaze glows over a light ground and nearly vanishes over a dark one, and Ultramarine over a yellow underlayer reads green. In our tests a thin Alizarin Crimson over white carries more chroma than its own masstone.
Fast enough to drag
Each layer is baked into a 17 × 17 × 17 colour table and applied by interpolation; in our tests the table matched the direct calculation within ΔE00 1.5 on random colours, and a thickness change re-rendered in about a fifth of a second.
Full-size export
Export PNG repeats the whole stack at the photo's full resolution, with the painted masks and scumble texture scaled to match.
Settings in the link
The layers (pigment, thickness, glaze or scumble, coverage and mask switch) are written into the page address; the painted masks and the photo are not.
Stays on your device
Your photo is decoded, glazed and exported by the browser itself, and no copy of it is sent to a server.
For painters planning glazes over an underpainting
Working painters, art students, digital painters with a pen and art teachers plan glazes over an underpainting.
Working painters
Working painters can photograph a dry underpainting and audition a two-layer glaze on its shadows before mixing.
Art students
Art students can swap the order of two glazes and see that ultramarine over sienna is not sienna over ultramarine.
Digital painters with a pen
Artists with a pen tablet can brush a glaze in with pressure, as lightly as they would on the canvas.
Art teachers
Art teachers can show the same glaze over white, grey and dark grounds to explain why grounds matter.
What a glaze actually does
A glaze is a thin film: light passes through it, strikes the paint beneath and returns filtered, while the film itself scatters a little light of its own colour. A clear glaze over a light passage deepens and hues it, which is why glazed passages look lit from behind; over a dark passage there is little light left to filter, so the same glaze barely shows.
Kubelka–Munk theory describes exactly this: a layer of given absorption and scattering over a background of given reflectance. The simulator computes it for every layer over the colour beneath, so the ground and every earlier layer shape what the next glaze does.
Layers, order and optical mixing
Depth in glazing comes from repeated thin films, each dry before the next. Two layers of different pigments mix optically, not on the palette: a blue glaze over a yellow underlayer reads green, and the order matters, because each film is judged over what is already there. Swap two layers with the arrows to see the difference.
Use the thickness slider to rehearse restraint: if a single film of Alizarin Crimson already takes a shadow near black, the next layer belongs elsewhere.
Glaze or scumble
A scumble is the opposite move: a thin, broken layer of lighter, more opaque paint dragged over a darker passage so the layer below shows through the gaps. It lightens and softens, where a glaze darkens and enriches. In Scumble mode the film lands in a dry-brush texture, and Coverage sets how much of the passage catches paint. Titanium White scumbled over a shadow gives the veiled, atmospheric grey painters use for haze.
Brushing a layer on
Glazes are rarely global: the shadow side of a face, the depths of drapery. Turn on Only where I paint and brush the layer on; each layer keeps its own mask. The brush has a soft edge, and with a pen each dab applies only as strongly as you press, so a light touch lays a faint glaze and a firm one the full film.
From preview to palette
The pigment colours are masstone approximations, and real glazes depend on pigment load, medium and brand, so take the exported plan to the easel as a target, apply thinly and judge in your painting light. A study from the underpainting generator makes a matching base image. The paint mixing simulator mixes a glaze colour from two or more tubes.
Further reading
The page below goes further into the ideas the Glaze Layer Simulator works with, and opens on the site named beside it.
- Glazing techniques and layered painting methods (ArtisticMasterclass.com)
Tips from a working artist
From Sujith Puthran, artist and founder: what I actually do at the easel.
Glaze over light passages for glow; over darks a glaze mostly deepens, so keep the underpainting lighter than the final value.
Two thin films in different pigments read richer than one mixed film; try both orders.
Keep one unglazed darkest dark so the passage keeps its punch.
Scumble white or a pale colour over a background to push it back; keep Coverage low for a light veil.
Always test the glaze on a corner of the actual painting; the preview shows direction, not destiny.
Why your picture stays on your device
The Glaze Sim is a program your browser downloads and runs by itself. When you choose a picture, the browser reads it from your files and does the work on your own phone or computer; no copy is sent to this site or to anyone else, and what you export is saved straight from the browser. That is why there is nothing to upload and nothing to sign up for. The privacy page says what the site does collect.
Questions about the Glaze Layer Simulator
The 5 questions below cover why a glaze changes with its ground, accuracy and lightening, then the base image and pen pressure.
The theory
Why does the same glaze look so different over different grounds?
The same glaze looks so different over different grounds because a glaze filters the light coming back from below. A light ground returns plenty of light for the film to colour; a dark ground returns little, so the film shows mostly its own faint scatter. The stack swatches under the stage show one set of layers over white, grey and a dark.
Is this physically accurate?
Partly: this is physically accurate in its method, which is the standard Kubelka–Munk model for a film over a background, on reflectance curves estimated from each paint's masstone colour. It reproduces how glazes depend on the ground, how layers mix optically and how thick films approach the masstone. It does not know each tube's real transparency, oil content or brand, so treat it as a plan.
Can a glaze lighten a passage?
No, a true glaze cannot lighten a passage; it only filters. A light opaque paint can, which is what Scumble mode is for.
Using it
What should I load as the base image?
Load a photo of your actual underpainting as the base image, since that is what the glaze will sit on.
Does pen pressure work with a mouse?
No, pen pressure does not work with a mouse: a mouse or finger always paints at full strength. Pen pressure comes from a stylus on a tablet or touchscreen that reports it.
Load a photo of your underpainting, stack glazes and scumbles, and brush them where they belong.
Free · No sign-up · Runs in your browser