Repost: Glazing

Among oil painters, there seems to be a com­mon mis­con­cep­tion that glaz­ing is some kind of mys­ti­cal tech­nique that only a few can mas­ter. The basic process is, how­ever, very sim­ple. Glaz­ing is putting one layer of paint over another so that you can see the under­layer through the upper layer of paint. Glaz­ing is a form of indi­rect paint­ing, which just means that you are paint­ing with more than one layer, allow­ing pre­vi­ous lay­ers to dry before you add more paint on top.

Glaz­ing can be used for a num­ber of pur­poses. As I noted my post com­par­ing the glaz­ing meth­ods of Ital­ian and Nether­lan­dish Renais­sance painters, glaz­ing can be used to cre­ate opti­cal color mix­tures (a blue glazed over a yel­low makes a green) or to cre­ate mod­el­ing effects (thicker lay­ers of trans­par­ent paint are darker, so you can adjust value by adjust­ing the thick­ness of the paint). Some artists glaze over a whole paint­ing to unify the over­all tone. Oth­ers will glaze spe­cific parts of the paint­ing. One method is to do an ini­tial monot­one under­paint­ing (in shades of grey, for exam­ple) then apply color over it. This sim­pli­fies the process of paint­ing by first tack­ling pure value, then work­ing out hue and chroma. Some mod­ern por­trait painters will do an ini­tial paint­ing of flesh in shades of green (they incor­rectly call this a “ver­dac­cio”). They then glaze with reds and oranges (com­ple­men­taries and near-complementaries to green), pro­vid­ing the flesh tones with a sense of vital­ity that is dif­fi­cult to achieve with direct paint­ing. Glaz­ing can also be use­ful for main­tain­ing chroma in light col­ors. Mix­ing with a lot of white will seri­ously reduce the chroma of most col­ors, result­ing in a look often described as “chalky.” If you glaze the same color over white, how­ever, you can achieve an opti­cal effect that is high in value, with more chroma that you could get by mix­ing that color with white.

Because a glaze dark­ens what it cov­ers (unless it’s a scumble—see below), it is best to do the under­paint­ing lighter than the intended final effect. If you are going to glaze, it’s impor­tant for the under­paint­ing to have as smooth a sur­face as pos­si­ble. That’s because irreg­u­lar­i­ties will trap excess amounts of paint in the glaze layer, cre­at­ing weird lit­tle spots of darker paint. So, before the paint dries, it’s a good idea to go over it very lightly with a soft dry brush, look­ing for lumps and gen­tly brush­ing them down. After the under­paint­ing has dried thor­oughly, you may want to wet sand to cre­ate as smooth a sur­face as possible.

In select­ing paint col­ors to glaze with, it is use­ful to dis­tin­guish among opaque col­ors (like cad­mium yel­low), semi-transparent col­ors (like ultra­ma­rine blue), and trans­par­ent col­ors (like alizarin crim­son). While any of these col­ors can be used for glaz­ing, trans­par­ent and semi-transparent col­ors are darker when they are put on more thickly. Opaque col­ors can be used for glaz­ing, but only when they are applied in a thin layer. A thick layer of an opaque color is not a glaze, because you can’t see the under­paint­ing through it.

Many oil painters think that the best way to glaze is to dilute the paint with medium to a watery or syrupy con­sis­tency (this is what a lot of art instruc­tion man­u­als tell you to do). The paint becomes less opaque because the pig­ment par­ti­cles are sep­a­rated by a larger than nor­mal amount of trans­par­ent vehi­cle. This type of glaze is called a dilu­tion glaze. In my (deeply hum­ble) opin­ion, it’s the wrong way to glaze. It’s bad tech­nique for (at least) three rea­sons: (1) all of that extra resin and oil will darken and yel­low over time, ruin­ing the effect; (2) dilu­tion glazes tend to cre­ate a sort of “tinted pho­to­graph” effect that doesn’t have the solid­ity a painter is usu­ally try­ing to depict; and (3) the doc­u­men­ta­tion I’ve found on his­tor­i­cal glaz­ing tech­niques sug­gests that only small amounts of resin are detected in glaz­ing lay­ers in Renais­sance Nether­lan­dish paint­ings, which I con­sider to be the gold stan­dard in glaz­ing for both beauty and longevity.

A bet­ter method is called a reduc­tion glaze. This approach involves adjust­ing the trans­parency of the paint by adjust­ing the thick­ness of the paint layer. While you can do a reduc­tion glaze with noth­ing but pure oil paint, it helps to first lubri­cate the sur­face by apply­ing a very thin layer of a slip­pery medium. My pre­ferred glaz­ing medium is a 50/50 mix­ture of black oil (lin­seed cooked with lead) and Venice tur­pen­tine (if you don’t like to use sub­stances con­tain­ing lead, lin­seed oil will work almost as well). Stu­dio Prod­ucts also sells an excel­lent glaz­ing medium. You can also use plain lin­seed or wal­nut oil as a glaz­ing medium. Put a drop of medium on the sur­face, rub­bing it in with your fin­gers to spread it as far as pos­si­ble. This way, you can cover a large area with just a few drops of medium. In addi­tion to putting some on the sur­face, you can also put just a tiny bit of medium in your paint, but I don’t usu­ally find that necessary.

Mix up the color you want to glaze with. Apply it thickly and evenly to the desired area with a brush. It will look like a hor­ri­ble mess at this stage, but have faith. You will now reduce the thick­ness of the glaze to the desired opac­ity and value. Do this by dab­bing with a soft brush, smear­ing with your fin­gers, rub­bing with a cloth or sponge, or what­ever works to adjust the glaze to achieve the desired effect. With a lit­tle prac­tice, a reduc­tion glaze is really pretty easy. You can get nice gra­da­tions in color and value by cre­at­ing a gra­da­tion from thin to thick. Or you can cre­ate gra­da­tions from one color to another. Once you have the glaze spread to the right thick­ness, you can, if you like, paint into it with other col­ors. For exam­ple, you can apply light high­lights into a wet glaze and then blend it in. If desired, you can let your glaze dry and then add one or more addi­tional lay­ers of glaz­ing. For exam­ple, you can get really intense, chro­matic darks by glaz­ing with mul­ti­ple lay­ers of trans­par­ent paint.

When mix­ing col­ors for a glaze, it is some­times help­ful to add a small amount of white to your mix­tures. This pro­vides a greater sense of solidity.

If you glaze with very light col­ors con­tain­ing a lot of white, it is usu­ally called a scum­ble. Tita­nium white, being very opaque, can be a bad choice for scum­bling. Flake white and zinc white are much eas­ier to cre­ate trans­parency effects with. A very white, hazy glaze is called a velatura (“veil”). A velatura can be a great way to depict trans­par­ent smoke, haze, or fog.

Update

Instead of mak­ing sure the under­paint­ing sur­face is smooth before glaz­ing over it, you can delib­er­ately give it lots of tex­ture. Then the glaze will sink into the nooks and cran­nies, cre­at­ing a sense of dimen­sional relief. Rem­brandt often used this technique.