Grounds - Acrylic Resin Grounds

These acrylic primings are closely related in composition to the acrylic polymer tempera paints and are being universally employed as grounds for acrylic paintings. They are being increasingly used as grounds for the oil technique, as the lead-white linseed oil priming materials become more expensive and difficult to obtain.

The artist can make the acrylic ground material by combing the standard acrylic gloss medium or the acrylic emulsion Rhoplex AC-234 with titanium dioxide pigment and whiting. Add the binder to the pigment in the amount necessary to produce the familiar brushing consistency, slightly heavier than house paint. If a somewhat more absorbent ground is desired, thin the binder with water before adding it to the pigment. [pp. 109-110]

Equipment

Mixing Container
Stirring Rod

Materials

Binder. Acrylic polymer gloss medium or Rhoplex AC-234.
Filler:
1 volume of titanium dioxide dry pigment
2 volumes of whiting or precipatated chalk [calcium carbonate].

Procedure
1. Combine the titanium dioxide with the whiting in the mixing container.

2. Add the acrylic binder, slowly stirring it into the filler until a smooth paste, about the consistency of heavy house paint, is produced.

Notes
A. The proportion of titanium dioxide to whiting can be varied. Some acrylic priming is made without whiting, using only titanium. On the other hand, if exceptional whiteness is not a necessity, the proportion of whiting can be increased up to 4 volumes of whiting to 1 volume of titanium dioxide.

B. If a more absorbent ground is desired, the acrylic binder can be thinned with water, up to 1 volume of Rhoplex to 1 volume of water, before it is mixed with the dry filler. The proportions of water, acrylic binder, and filler should be noted and compared with the degree of absorbency of the priming. [Kay, Reed. The Painter's Guide to Studio Methods and Materials. Englewood Cliffs, NJ: Prentice-Hall, Inc., 1983. p. 110]

Procedure
1. Apply the first coat of priming so that it is brushed well into the weave of the textile. Smoother work will be obtained by thinning the acrylic priming, using about 1 volume of water for each 4 volumes of priming.

2. When the first coat has dried completely so that it has no wet streaks, a second coat may be applied at right angles to the first. Additional coats, applied in the same way at right angles to each other, improve the canvas. Prime the edges of the canvas that are folded over the sides and back of the stretchers. This protects the fabric against wear and raveling. The final coats may be applied with either the brush or a large palette knife. The use of the knife produces a surface that seems denser, resembling that of an oil-primed canvas.

3. Any roughness in the final surface may be removed by lightly rubbing it with fine sandpaper after the ground has dried well.

Notes
A. The acrylic priming has less body than does an oil priming of the same number of coats. This allows the weave of the fabric to be more conspicuous, causing the initial strokes of the painting to stand out with less relief on the prominent textile weave. Painters who find this unsatisfactory should apply more coats of priming, using as many as three to five coats on the fabric.

B. Since the acrylic priming does not contract upon drying as does rabbitskin glue, the canvas should be tightly stretched before the priming is applied. It may also be necessary to tighten the canvas after the priming dries by pulling out the tacks on two adjoining sides of the canvas and restretching the fabric.

C. If the fabric has an open weave, use acrylic medium or the acrylic gel medium to size it before applying the priming. Allow the sizing to dry thoroughly and then apply the acrylic priming as described in steps 1-3. The sizing prevents the priming from going through the weave of the fabric and forming lumps or beads on the reverse side that can cause irregularities on the front of the canvas.

D. Because it dries to the touch very quickly, artists sometimes begin to paint on the acrylic-primed canvas before it is thoroughly dry. To make sure that the canvas is free of moisture and that the ground has had a chance to set well, allow it to dry, whenever possible, for at least 12 hours before beginning to paint on it with oil colors or other mediums than acrylic tempera.

E. The acrylic priming does not always adhere well to oil-painted surfaces, and so the practice of priming over old oil paintings with acrylic primers is not recommended. The priming does adhere well to raw linen, cotton, paper, Masonite, or unpainted wood. [p. 111]

F. The acrylic-primed canvas can be used without further preparation for painting with acrylic colors. However, painters who intend to use it as a base for oil painting should be aware that repeated rubbing of the surface with liberal amounts of turpentine, or with paints containing high proportions of turpentine, may cause the ground to dissolve. Such solvent action can be avoided by using less turpentine, by applying the paint with a lighter touch, or by applying a very meager coat of flake white artists' oil color over the entire canvas surface with a palette knife, without thinning the paint with any solvent.

G. If portions of the acrylic-primed canvas are left uncovered by oil paint in the finished picture, these areas may be dissolved in cleaning procedures if organic solvents such as toluene, xylene, acetone, or turpentine are used. Accordingly the painter should note on the edge of the excess canvas turned over the back of the stretcher strip that the priming contains acrylic resin and that it should be cleaned with care.

[pp. 111-112]