Glazing in watercolour is the practice of applying one thin, transparent wash over another that is completely dry. Done well, it builds colour depth and luminosity that no single flat wash can produce. Done carelessly, it flattens colour, lifts the underlayer, and leaves the painting looking overworked. The difference lies almost entirely in pigment choice and patience.
At a glance
Glazing only works with transparent pigments. An opaque pigment glazed over another colour produces a flat, chalky result. Check the transparency rating before you glaze.
Damp is not dry. A layer that looks dry may still be slightly wet on cotton paper. Wait until the paper feels cool to the touch and the sheen has gone before applying the next glaze.
Each glaze shifts the colour temperature. A warm glaze over a cool underlayer creates optical complexity. This is how glazing produces depth that a single flat wash cannot.
Three well-placed glazes outperform ten hasty ones. Overworking with successive glazes creates a dull, overworked surface. Plan each glaze with a specific purpose.
Staining pigments are permanent once dry. Phthalos and some quinacridones bond strongly to the paper. A glaze with PB15:3 cannot be lifted. Use with intention.
What glazing actually does to the surface
When light strikes a transparent watercolour layer, it passes through the paint film and reflects off the white paper surface beneath before returning through the paint to the viewer’s eye. Each successive glaze the light passes through modifies what the viewer perceives: the colour deepens, the tonal value drops, and, if the glazes carry different colour temperatures, the result has an optical complexity that mixed colour cannot replicate.
This is useful editorial shorthand rather than a precise optical claim. The practical point is that glazed passages can appear to have an inner glow because the white paper is still contributing to the reflected light, filtered through each transparent layer. Opaque pigments cut that process off. They block the paper surface. The result looks painted over rather than built up.
Glazing also allows selective adjustment without repainting. A passage that reads too cool can be warmed with a thin glaze of a transparent earth. A shadow that lacks depth can be deepened with a glaze of PB29 without touching the surrounding areas. This precision is what makes glazing a technique worth understanding properly rather than applying loosely.
Which pigments are suitable for glazing
Transparency is the single most important criterion. Watercolour manufacturers mark each colour’s transparency rating on the tube, typically using a square: solid black for opaque, half-filled for semi-opaque or semi-transparent, outlined for transparent. Trust those ratings. They reflect pigment behaviour, not marketing preference.
The most reliably transparent pigments include quinacridones (PV19, PR122), phthalocyanines (PB15:3, PG7), and some modern synthetics including the transparent pyrroles. Many of the traditional earth pigments such as Raw Sienna (PY43) and Burnt Sienna (PBr7) are semi-transparent and glaze reasonably well without deadening the underlayer. Cadmiums, titanium white derivatives, and most cerulean blues are opaque or semi-opaque and are generally unsuitable as glazing colours.
A practical working rule: if you can read text through a dried swatch of the colour on paper, it is sufficiently transparent to glaze with. If not, use it for first washes where its opacity carries less risk.
Staining behaviour also matters. High-staining pigments, including the phthalocyanines, bond to the paper surface very firmly once dry. This means you can glaze over them cleanly without fear of lifting. It also means that any glaze you apply using a staining pigment is permanent. Plan accordingly.
For a full guide to watercolour technique including which pigment families behave consistently across layers, the technique index covers this in more detail.
How to tell when a layer is genuinely dry
The most common glazing mistake is not the wrong pigment. It is impatience. A layer that is ninety percent dry will lift and streak when glazed over. The ten minutes saved by not waiting costs the painting.
There are two reliable tests. First, look at the paper surface under raking light. Any remaining moisture shows as a sheen. If the sheen is gone, that is a reasonable signal. Second, place the back of your hand against the paper. Evaporating moisture cools the surface. If the paper feels noticeably cool, even slightly, it is not fully dry. When the paper feels the same temperature as the surrounding air, it is dry.
Cotton paper holds moisture longer than wood-pulp paper and can appear dry on the surface while retaining dampness in the fibres. In a humid studio or on a damp day, add time. The tests above hold, but the margin for error is smaller.
Using a hairdryer speeds drying. If you do, let the paper cool completely before glazing. Heat changes the moisture reading. Glazing onto warm paper, even when genuinely dry, can cause unwanted flow behaviour in the new wash.
Building depth through successive glazes
A useful way to think about successive glazes is to plan by value rather than by colour. Begin with the lightest wash you need, which will become the lightest tone in the finished passage. Each subsequent glaze darkens the overall value. Work methodically: one glaze, assess, decide, glaze again if needed. Three purposeful layers produce a better result than six applied without a clear intention for each.
Colour temperature shifts are one of the most effective tools in glazing. Alternating between warm and cool glazes, without overloading any individual layer, produces the optical depth that painters describe as luminosity. A warm underlayer of PY43 or a transparent orange, followed by a cool glaze of PB29, creates a neutralised mid-tone with a visual complexity that a pre-mixed neutral cannot replicate. The colours remain distinct at a microscopic level while reading as unified at normal viewing distance.
Each glaze also requires a slightly different brush approach than a first wash. Use a loaded but soft stroke. A thirsty or scrubbing brush will drag at the surface of the underlayer even when it is dry, particularly on softer papers. A flat wash brush or a large round with a good belly and confident, single-pass strokes works best.
Where glazing goes wrong and why
Most failures in glazing trace to three causes: the wrong pigment, insufficient drying time, or excessive dilution of the glaze wash.
A glaze applied with too little pigment and too much water risks flooding the paper surface and pushing the new wash into unintended areas. It also risks creating a tide mark at the edge as the excess water dries. A glaze should be a thin wash, not a waterlogged one. Consistent, even dilution with a steady brush is more reliable than applying very wet colour and hoping it settles.
Overworking is a separate problem. Each glaze slightly reactivates the surface. A wash applied over four or five previous glazes, particularly on wood-pulp paper, can begin to loosen pigment from the lower layers and create a muddied, granular surface. The solution is to limit glazes to what the painting genuinely requires and to allow the earlier layers to fully bond before continuing.
Colour drift is also common. Successive warm glazes shift the overall hue progressively in one direction. Successive cool glazes do the same. Without periodic assessment at arm’s length, the cumulative effect can be stronger than intended.
What to buy
The following are reliable transparent pigments for glazing. All are available from major UK watercolour suppliers.
Transparent pigments
Winsor and Newton Professional
Quinacridone Magenta (PV19)
One of the most transparent single pigments available. PV19 glazes cleanly and retains its warmth and chroma through multiple layers. Useful for warm shadows, florals, and warm temperature glazes over cool underlayers.
Winsor and Newton Professional
French Ultramarine (PB29)
Transparent and granulating. PB29 works particularly well as a cool glaze over warm underlayers, producing the settled, slightly textured shadow quality that many painters associate with traditional watercolour. The granulation adds surface interest without muddying the colour.
Daniel Smith
Phthalo Blue (Green Shade) (PB15:3)
Extremely transparent and highly staining. PB15:3 is useful for building deep shadow glazes and achieving rich, saturated blues through layering. Because it stains strongly and cannot be lifted once dry, it requires confident application. Overuse creates a cool dominance that can be difficult to correct.
Where to buy
The practical verdict
Glazing is a controlled technique, not an intuitive one. It works when you understand the transparency of your pigments, respect drying time absolutely, and plan each layer with a specific tonal or temperature purpose. When those conditions are met, the results, particularly the luminosity of shadow passages built through alternating warm and cool glazes, are not achievable any other way.
The simplest rule: use transparent pigments, wait longer than you think you need to, and apply each glaze with a single deliberate stroke rather than working the surface. Every glazing problem is usually a version of one of those three things done wrong.