MATERIALS & METHODS - Painting - Oil Painting - Supports and Grounds
Rigid Supports:
Wood Panels - Cardboard - Standard Masonite Presdwood - Plywood - Metals - Grounds for Rigid Supports
Flexible Supports:
Paper - Textiles - Commercial Products - Grounds for Flexible Supports
Preparation of Wood Panels
with Glue Gesso
Equipment
Materials
Although it may vary, 2 pounds of filler usually fills a quart measure; thus the proportions will be approximately:
[p. 116.]
2. Size the panel, front and back, using the recipe and procedures described in the section on sizing the flexible support. Allow the sized panel to dry thoroughly [at least overnight].
3. Soak the glue for gesso in water a minimum of three hours [overnight is better] until it swells.
4. Warm the glue in the double boiler until it is completely dissolved. Do not boil the glue. Remove it from the stove when it is dissolved. The double boiler will keep it warm and liquid for a long time. If it should cool and thicken later, put it back on the stove and heat it gently.
5. Slowly sprinkle the filler into the warm glue. Avoid adding large amounts of filler too rapidly, or air bubbles will form. As the filler is added, it absorbs the glue-water and settles to the bottom. When all the filler has been put into the glue-water, a small island of dry filler may remain uncombined in the middle of the glue-water, and this should be stirred gently into the mixture.
6. Next, stir the mixture gently to be sure it is smooth and there are no lumps of unmixed filler at the bottom of the container. The two-inch bristle brush can be used for this purpose. Stir slowly and avoid the formation of bubbles. The white mixture should be the consistency of heavy milk or light cream. If there are gritty white granules in the mixture [caused by roughly ground zinc or titanium white in the filler], pour the whole batch into another clean pan or bucket. Wash out the top section of the double boiler with warm water and fasten a double layer of cheesecloth over the rim, using string or an elastic band to hold it [p. 117] firmly. Slowly pour the mixture through the cheesecloth back into the top section of the double boiler. Smooth out any lumps by rubbing them against the cheesecloth with a brush or spoon. After straining the mixture, discard the cheesecloth and wash out the brush. The gesso should now be smooth and ready to be applied.
7. Apply the mixture to the sized panels. The first coat should be applied thinly, scrubbed or stippled on with a brush that is not too full, thus providing a surface on which the subsequent coats can hold.
8. Just as soon as the first coat is dry to the touch, apply the second coat with even strokes parallel to one edge of the panel.
9. Apply the third coat as soon as the second coat is dry enough to be painted over without being picked up. The direction of the strokes should be at right angles to the previous coat.
10. Apply the fourth and fifth coats in the same way as step 9, each coat running at right angles to the preceding one.
11. When possible, apply coats of gesso to the back of the panel, with one coat on the back being applied for each on the front, as soon as the front coat has dried enough to be handled. This helps to make the tension equal on both sides of the panel, and so it is less likely to wrap.
12. When the panel is thoroughly dry, smooth it well with fine sandpaper to eliminate all ridges and lumps. Dust the panel well before using.
[pp. 117-118]
Notes [On the preparation of panels]
A. An alternative method for making the gesso requires the preparation of the filler and the glue water as described before in steps 1-4. Put the dry filler into a clean pot .
Then slowly add a small amount of glue to the filler and stir to make a smooth stiff paste, free of lumps.
Gradually add more glue, stirring the mixture slowly, until it is the consistency of heavy milk. Stir gently and avoid bubbles. If there are heavy white granules in the mixture [from roughly ground zinc white], strain the gesso through cheesecloth to produce a smooth consistency, as in step 6.
B. If the gesso can be rubbed off very easily by sandpaper, not enough glue was used in the mixture and more should be added. If the gesso sands with too much difficulty, there is an excess of glue present; therefore whiting, mixed with a little warm water, should be added. It is wise, before applying the gesso to the panels, to try it on a piece of scrap wood or Presdwood, testing it with sandpaper to see if the gesso is the right strength.
C. Casein or gelatin solutions may be used to replace rabbitskin glue solution in the gesso, but the rabbitskin glue is superior in flexibility and toughness to the other materials. [See section on casein for the recipe.]
D. Whiting may be used alone, without the addition of zinc or titanium white, but it will not be as opaque and white. [p. 118]
E. Precipitated chalk may be used as the filler instead of whiting, but this artificially manufactured calcium carbonate is lighter and fluffier than natural whiting, and the recipe should be adjusted for the substitution. In combination with 1 quart of the glue water described before, about 3/4 of a pound of precipitated chalk will be needed. The dry chalk will bulk approximately 24 ounces by volume. A substitution of titanium or zinc white for 10 percent of the volume of the chalk will increase the covering power of the gesso.
F. About 3 ounces of gesso is required to cover a square foot of Masonite with four coats. Thus 1 1/2 quarts of gesso, as made by the recipe in steps 1-12, should cover a panel approximately 4 by 4 feet, with four coats. This figure will vary, depending on the heaviness of the coats.
G. The number of coats may vary with the requirements for the particular job and with the skill of the craftsman. Sometimes as few as two are used; sometimes as many as ten. Two thinly applied coats are more effective and will look better than one heavily brushed coat in which brush strokes show.
H. The gesso will froth or bubble violently if it is stirred too vigorously or heated too much, and consequently pinholes or small blisters will appear in the coats on the panel. These are almost impossible to remedy with subsequent coats. Keeping the gesso to a medium warmth and stirring gently helps to avoid pinholes. To some extent a small amount of ox gall [about 1/4 teaspoonful to a quart of gesso helps break the surface tension that causes the bubbles.
I. The gesso should be stirred frequently but gently to keep the filler from settling to the bottom of the container. [p. 120]
J. If no scale is available for weighing the glue, the proportions of the recipe can be approximated by the following method:
b. Gently add dry rabbitskin glue until the level of water rises an additional 2 fluid ounces-- that is, up to the mark that indicates 18 fluid ounces.
c. Put the glue-and-water mixture into the double boiler and add to it 16 fluid ounces of water, to bring the total volume to 32 ounces of water plus the immersed glue.
d. Allow the glue to soak 3 hours, or overnight if possible. Then heat and dissolve the glue as in step 4 for making glue gesso and combine it with the filler as in steps 5 and 6.
When it is first put into water, 1 ounce by weight of glue usually displaces 3/4 ounce [by volume] of water.
K. Heavy grooves are caused by applying the coat too thickly or rebrushing the gesso too much as it begins to set up on the panel.
L. Panels may be finished to a very smooth surface by the following method:
b. Fold it neatly into a pad about 3 by 3 inches.
c. Polish surface of panel with the damp pad, working in even, small, circular strokes, going rather rapidly across the panel. Do not [p. 121] polish too long in one spot, or the gesso will be dissolved right down to the support.
M. Whenever layers containing glue solution [whether in gesso, gilding mixtures, or distemper paints] are applied one over the other, it is best to keep the glue at the same concentration through all the coats. If a stronger glue solution is painted over a weaker one, it will crack badly.
N. If continued heating drives some of the water out of the gesso after several hours of work, add a little warm water to keep the glue from getting too strong [see preceding note]. If the final coats are a trifle weaker than the earlier ones, no harm is done.
O. Glue gesso, like all mixtures containing animal glue, will decompose within a rather short time. Stored in a clean container and in a cool place, it will gel and may be kept for several days. As soon as it begins to spoil, it will have a bad odor and must be discarded. In any case, it should not be kept more than two weeks. To restore the gelled gesso to liquid state, simply heat it again in the double boiler.
P. Gesso can be applied to heavy rag cardboards by the same procedures outlined before for presdwood and wood panels.
Q. Raw linen or paper can be mounted on a rigid panel of Presdwood or plywood by using a rather strong solution of rabbitskin glue [3 ounces by weight of glue to 1 quart of water--soak overnight and heat gently]. It can then be gessoed in the usual way. The glue should be brushed over the panel rather liberally. The textile should be dipped in the glue solution, and the excess glue squeezed out. While the panel is still wet, the textile is spread over it and smoothed flat by rubbing from the center toward the edges to press out the bubbles. Excess fabric is folded over the edges of the panel and pressed to its back. The panel should be allowed to dry well [overnight] before it is coated with the gesso. Such panels need no additional sizing before the gesso is applied and usually receive only a thin application of gesso, so that the weave of the textile is not totally obscured.
[pp. 118-122]
[Kay, Reed. The Painter's Guide to Studio Methods and Materials. Englewood Cliffs, NJ: Prentice-Hall, Inc., 1983.]
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