Glazing With Acrylics: Method, Mediums and Mistakes

A glaze is a thin, transparent layer of color laid over paint that has already dried. The color underneath shows through and mixes with the glaze in your eye rather than on the palette, which produces depth you cannot get by mixing the same two colors together first.

It is the single most useful acrylic technique that beginners skip, and it is not difficult. What follows is the method, the mediums, and the specific things that go wrong.

Use a medium, not water

This is the decision that determines whether glazing works for you.

You can thin acrylic with water and it will become more transparent. But water thins the binder along with the color, and past roughly a quarter water by volume there is not enough acrylic left to hold the paint to the surface. The result is a weak film that can lift when you glaze over it, and colors that look chalky rather than luminous.

A glazing medium is mostly acrylic binder with no pigment. Add as much as you like — the film stays sound however transparent you make the color. That is the whole reason mediums exist.

• Glazing liquid — formulated for exactly this, usually with a retarder included so you get longer to work. The default choice.
• Gloss medium — thinner and faster-drying, no retarder. Good when you want the layer set quickly.
• Fluid or high-flow acrylic mediums — for very thin, watery glazes that still keep a proper binder.
• Gel medium — thicker, holds a brushmark, for glazes with body.

Matte versions of any of these contain a matting agent that slightly clouds deep colors as it builds up. For glazing over darks, use gloss and adjust the final sheen with varnish at the end.

Two things not to use: glycerin, sometimes suggested as a homemade retarder, which can leave the film permanently soft; and solvents of any kind. Turpentine, mineral spirits and oil of spike lavender belong to oil painting. On acrylic they break the film down.

Ratios

There is no correct formula, and articles that give one precisely are guessing. What matters is the proportion of pigment to medium.

Start at roughly one part paint to four or five parts medium and adjust. More medium gives a more transparent, subtler glaze that you build in several passes. More paint gives a stronger shift in one go, with less control.

Mix it in a container, not on the canvas, and mix more than you think you need — matching a glaze halfway through an area is unpleasant.

Choose transparent pigments

Some pigments are naturally transparent and some are opaque, and no amount of medium turns an opaque pigment into a good glaze — it just goes milky.

Quinacridones, phthalos and most of the "hue" versions of traditional lake colors glaze beautifully. Cadmiums, titanium white and the earth opaques do not. Manufacturers print a transparency symbol on the tube, usually a solid, half or open square. Look for it before you buy.

The method

1. Let the layer underneath dry completely. Not touch-dry — properly dry. Glazing onto paint that is still curing lifts it and muddies both layers.
2. Lay the painting flat. A glaze is thin enough to run, and a canvas on an easel will pool color along the bottom edge of every area.
3. Apply with a soft, flat brush. Synthetic is fine and easier to clean. Stiff bristle leaves streaks that the transparency will show up rather than hide.
4. Work in one direction across the area, then stop. Brushing back and forth into a setting glaze is what creates streaks.
5. Wipe back while it is still wet if you want variation — a soft cloth lifting glaze off the raised parts of the surface leaves it sitting in the low parts, which reads as depth. You have a minute or two at most, so decide before you start.
6. Let it dry before the next glaze. Thin layers are usually ready in under an hour, but touch it first.

Build up in several weak glazes rather than one strong one. Three subtle passes look like light. One heavy pass looks like a filter.

What glazing is actually for

• Shadows that stay luminous. A transparent dark glaze over a color darkens it without deadening it, which black mixed into the paint always does.
• Unifying a painting. A single weak glaze over everything pulls disparate colors into the same light.
• Adjusting after the fact. A picture that has gone too cool can be warmed with a thin warm glaze rather than repainted.
• Soft transitions. Acrylic dries too fast for easy wet blending. Overlapping glazes gets you gradients that are hard to achieve any other way.

The background matters. Glaze over a light ground and the light passes through the color and bounces back, which is what "jewel-like" means. Glaze over a dark ground and most of that light is absorbed, so the effect is much quieter.

Mistakes that ruin a glaze

• Glazing over paint that is not dry. The most common one by far.
• Too much pigment. If you cannot see the layer underneath, it is not a glaze — it is a thin coat of paint.
• Using water as the thinner. Covered above, and the reason most first attempts look chalky.
• Reworking it as it sets. Put it on, adjust it immediately, then leave it alone.
• Working on a rough surface. Heavy canvas texture collects glaze in the weave and looks blotchy. Fine-weave canvas or a smooth panel is far more forgiving.

Glaze and varnish are not the same thing

A glaze is transparent color and part of the painting. Varnish is a clear protective coat applied at the end, and it is meant to be removable so the surface can be cleaned decades later.

A final all-over glaze will change every color underneath it. If what you want is protection, use varnish, once the paint is fully cured — which takes days, not hours.

Glazing a paint by numbers canvas

You can, and on a finished kit it is a genuinely good way to make the result look less flat.

Once the canvas is completely dry, a weak glaze over a shadow area softens the hard edges between numbered sections, which is the thing that most makes a finished kit read as a kit. Work quietly and test on an inconspicuous corner first.

Our notes on layering acrylic paint cover building up in stages, and the color wheel helps with deciding which glaze color will do what you want. If you want a canvas to try it on, there is the full range of kits and a custom option from your own photograph.