Oil Painting - Mediums

The majority of experienced painters prefer to mix their own glaze mediums because so many of the ready-made mediums of the shops are put out as secret formulas without a clear statement of all their ingredients. Variations or adjustment of homemade mixtures to suit individual requirements is easy; with ready-prepared mediums it is dangerous. [p. 109] [Mayer, Ralph. The Painter's Craft. An Introduction to Artist's Methods and Materials. Revised and updated by Steven Sheehan, Director of the Ralph Mayer Center, Yale University School of Art. New York: Penquin Group. 1948. 1991.]

A different character of glaze or scumble may be obtained by thinning the paint with a diluent or glazing medium, so that it need not be rubbed. This medium may be made up of various combinations of oils, varnishes, and volatile solvents. As in the case of the painting medium, the personal requirements of each artist must determine the exact composition of such a medium [with particular attention to the composition--such as to whether or not there is too much turp or the glaze is "leaner" than the dry underpainting--and it is important that "fatter" glazes don't discolor the transparency of the glaze due to excessive oil or due to impurity of old oil or color of the type of oil in the medium--this is a very real problem to take into consideration] . A painter who wishes to glaze rather heavily and to obtain an even vitreous film over an area may want to glaze medium that can be applied evenly and rapidly to the picture surface. The artist may also want the glaze to set quickly so that the picture may be placed upright in a short time without the paint's trickling. Such rapid setting mediums contain varnish or driers or both, along with the oils , and require a certain skill in handling, since they quickly become tacky and then cannot be reworked or easily removed.

A typical recipe for a rapid setting medium is:

3 parts of volume of stand oil

2 parts by volume of dammar varnish (5-pound cut)

3 parts by volume of turpentine 1 or 2 drops of cobalt drier per pint of medium

Another painter may prefer a slower setting material so as to be able to deepen or lighten it, remove it or add to it, or reinforce modeling transitions with it. Such a slower medium might consist solely of stand oil with a little turpentine added.

In general, the less medium used, the better. The glaze or scumble should be made lighter or thinner by dispersing or rubbing rather than by adding excessive amounts of glaze medium as a diluent.

When discussing the merits or disadvantages of a given glazing medium, one must keep in mind the way it is to be used. If only small amounts of medium are added to conventional tube colors, such factors as the yellowing of a particular oil (sun-thickened oil, for example) or the possibility of redissolving a soft resin varnish (such as dammar) are much less hazardous than they would be if the painter were to use large amounts of the medium in proportion to the tube color. The practice of adding glaze mediums to oil paint until it has the consistency of a watercolor wash seems to me to be unnecessary and to magnify all the technical dangers of the oil technique. The desired effects can usually be obtained with less medium and more skill. [pp. 79-80]

Notes
A. The glaze or scumble actually accentuates all brush marks and surface irregularities in the underpainting. Thus the character and direction of all strokes in the underpainting should be meaningful and consistent with the painterÍs purpose. [p. 80]

B. Colors diluted with too much glaze medium may trickle. Sometimes such over-thinned color develops small spots in the dry film which look like dust spots. Actually they are particles of color clumped together like islands of pigment in a sea of oil.

C. The underpainting must be bone dry before it receives a glaze or scumble.

D. Glazes containing so much medium as to create a glassy surface are dangerous, since subsequent films cannot adhere well to them and must crack at the first movement of the canvas.

E. Glaze films containing high amounts of spirit-resin varnishes (such as dammar) in relation to the oil and pigment content are extremely vulnerable to cleaning operations, since the varnish is always resoluble in the cleaning agents used by most restorers. Glazes that are the final or finishing films on a picture are especially vulnerable since they are usually thin.

F. Pictures glazed with slow-drying colors and very slow-drying mediums (such as walnut oil or poppyseed oil) should be shielded from dirt and dust while they dry.

G. Unsuccessful scumbling or glazing effects may be removed while the glaze is still fresh without disturbing the underpainting by wiping the surface with a clean, soft, lintless rag, moistened, if necessary, with a little turpentine. Such removals are possible only if the underpainting was thoroughly dry before the glaze was applied.

H. Any changes in the mediums in the glazing or scumbling of a particular area will be apparent--can be advantageous as well as very disadvantageous. [pp. 80-81]

Technical Procedures
Technical complication and variety increase with indirect painting. One method frequently employed may be described in the following general terms:

1. A brush drawing involving only one or two colors is developed to mark out the important locations and divisions on the canvas. The paint is thinned by means of a "lean" medium [such as 1 part sun-thickened oil, 1/2 part varnish, 3 parts turpentine] to a brushable consistency which flows rather easily.

2. The dark and light contrasts are developed by the use of a "lean" fast-drying white [such as flake white] in all the light areas. In the middle tones the white is mixed slightly with another pigment [ocher, for example, or Indian red]. Darks are produced by adding more color or mixed grays to the white, but all darks are kept much lighter than they will appear in the finished painting. The main effort, at this point , is to produce strong placement and gesture of shapes and volumes. These should be expressed broadly with little surface detail but should be accurate as to the relationships of the larger major pictorial masses. At this stage, the effect of this underpainting must be lighter, both in the lights and the darks, than the artist wishes the finished picture to be.

3. When this underpainting has dried thoroughly, color relationships are developed over the light monochrome by the use of glazes. These may be brushed on and [p. 81] then modified by wiping them down with a rag or a clean brush so that they emphasize and reinforce the drawing and movement of the underpainting.

4. Color effects are strengthened and made more definite by vigorous direct painting into the glazes [either when the glaze has dried or while it is still wet] with substantial strokes of opaque color. Glazes that have lowered the tone of an area too much may be scumbled over with a lighter color to raise their tonality. Drawing and edges are redefined, especially where glazing or scumbling has caused a passage to lose its initial strength. [pp. 81-82]