What "Glazing" Actually Meant — Then vs. Now

There are 58 passages in our corpus that discuss glazing. They come from eight different books spanning 1390 to 1920. Read together, they describe the same technique in remarkably consistent language. Read against most contemporary "glazing" tutorials, they describe something almost entirely different.

This essay is the side-by-side.

What the classical books say it is

The longest and most precise account is in Solomon's The Practice of Oil Painting (1910), Chapter XII — Colouring a Monochrome. The procedure has four parts:

1. A complete monochrome underpainting. The painting is fully resolved in grisaille — a warm grey or brown — before any color is introduced. Values are locked. Forms are modeled.
2. The underpainting must dry completely. Solomon says days, sometimes weeks for thicker passages. Glazing a wet or partially dry underpainting destroys both layers.
3. A transparent glaze is laid over the dry underpainting. The glaze is paint thinned with medium to the point of transparency. The lower painting shows through, modified by the glaze. The optical effect is light passing through the upper layer, bouncing off the lower, and back through the glaze again — twice modulated.
4. The glaze is left alone. No working into it after it has been laid. Each glaze is allowed to dry before another is considered.

Vibert (The Science of Painting, 1892) is the chemistry. He describes which pigments are transparent enough to glaze with (madder, alizarin, the umbers, viridian, the lakes) and which are opaque and cannot (the cadmiums, the lead whites, the earths beyond a certain mixing ratio). The pigment selection determines what color you can achieve through glazing — and what colors require a different technique entirely.

Cennini, from 1390, describes substantially the same procedure in egg tempera, six hundred years before Vibert. He calls the underpainting verdaccio and the upper layers velatura. The terminology shifts. The technique is identical.

"In red conté chalk and white pastel rubbed on toned paper.… The glazes that follow tint the monochrome as water-colour tints an engraving — they do not paint over it, they pass through it." — Speed, The Practice and Science of Drawing

The key word in every classical account is transparent. A glaze is transparent. If it is not transparent, it is not a glaze. It might be a scumble, a wash, a wet-in-wet pass, an opaque overpaint — but it is not a glaze. The word means a specific thing.

What "glazing" usually means now

Pick any of the top YouTube painting tutorials that use the word glaze. You will find some combination of the following:

• "Add a glaze of crimson over the cheek" — applied wet over wet, often before the lower layer is dry. This is not glazing. This is a wet-in-wet color mix.
• "Use glazing medium to thin your paint" — sold as a general consistency thinner, not as part of a layered procedure. The medium is real, but using it does not make the resulting layer a glaze.
• "Glaze the shadows" — applied as the primary shadow color rather than over a fully-resolved value structure. The shadows in such a painting are unsupported by an underpainting; there is no value scaffold beneath the color to glaze onto.
• "Glazing is a fast finishing technique" — implying it can be done in the same session as the rest of the work. The classical books are unanimous that it cannot.

The word survived. The procedure it described — a sequenced, multi-day, dry-layer-only laminated painting — mostly did not.

Why the technique fell out of common use

Two real reasons and one false one.

Real reason 1: alla prima painting became the default. The Impressionist generation in the 1870s and 1880s painted predominantly wet-into-wet, often finishing a canvas in a single session at the easel or in the open air. This was a deliberate stylistic choice — capturing transient light required speed — but it also became the dominant teaching approach in the twentieth century. Once you teach a generation of painters to work alla prima, they teach the next generation the same way, and the layered procedure is no longer transmitted.

Real reason 2: lead white was banned. Lead white has properties that make classical glazing work — it dries faster than other whites, has a specific transparency profile when thinned, and binds layers chemically in a way titanium does not. When lead white was effectively banned as an artist pigment in the late twentieth century, the substitute (titanium or zinc) changed the working chemistry. Glazing over a titanium-white underpainting is harder than glazing over a lead-white one. The substitution is honest, but it is not equivalent.

False reason: "it's too slow for modern painters." Painters who cite this are usually conflating elapsed time with easel time. Glazing requires elapsed days because of drying intervals. It does not require many hours at the easel — a glaze pass is often 30 to 90 minutes of actual painting. The total elapsed time is the issue; the labor is not. Modern painters who manage to be patient about anything — varnishing, framing, oil-paint drying — can manage to be patient about glazing.

What our recreation guides do with this

We picked Solomon as the primary technical source partly because he is the most cited book in our corpus (every one of 2,491 guides references him), and partly because his account of glazing is the clearest of the ten. When a recreation guide says "apply a transparent glaze of viridian over the dried grisaille (Source 1)", Source 1 is a specific chapter of The Practice of Oil Painting. You can look it up. You can disagree with it. You can read the rest of the chapter and decide what Solomon thinks the next step should be.

The recreation guides for Vermeer, Reynolds, Bouguereau, the late Titians, and roughly 1,955 of the 2,491 paintings in our corpus include explicit glazing or scumbling steps. The pipeline detected those steps in the source passages and routed them into the structured output. It did not invent them.

A note on terminology: we're not arguing the modern usage is wrong, exactly. Words drift. But two different procedures sharing a word makes it hard to be precise about which one you're trying to learn. When the recreation guides on Apprentice say "glaze," we mean the classical procedure — transparent layer over dry underpainting, days of drying between. That's the version Solomon describes. It's not the only version, but it's the one the masters used, and it's the one our citations point at.

Solomon's chapter is free at sources. The Vermeer recreations in the collection are the cleanest place to see the procedure laid out step by step.