Auxiliary Supports
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Auxiliary Supports(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987) The purpose of an auxiliary support is to give structure and support to the support itself. An auxiliary support may be either stretcher bars, a frame, or a panel. A panel is a uniform structure with at least one solid, flat, unbroken surface. The first panels were made of wood planks butted against each other, the surface of which was used to paint on. Today, lightweight panels are used as auxiliary supports as well as supports. A frame consists of a set of bars that are fixed together and cannot be expanded. Frames were first seen in the seventeeth century Dutch school of painting. Their introduction was a major advance in reducing the weight and increasing the portability of paintings. Stretcher bars are bars designed to produce a frame that can expand slightly to tighten further a stretched canvas. The first stretcher bars with mitered corners and keys (little wedges used to force open the corners of a stretcher bar frame to tighten a stretched canvas) appeared in the early nineteenth century. Frame Supports are the simplest and the oldest auxiliary support for stretching canvas. They are the easiest to make, but they have no provision for tightening sagging canvas. They consist of four pieces of wood in small sizes, which are simply glued and nailed together. Cross braces are added for larger sizes. Today, frame supports are made from kiln-dried pine or mahogany, which has less tendency to warp. The bars are usually made from 1" x 2" lumber that has had one of the 1-inch sides milled at an approximately 30-degree angle to produce a ridged edge. The ridge allows the canvas to be stretched with only one edge of the bar touching it, rather than a whole side, which could leave an unsightly impression on the front of the canvas. The corners and cross braces are often reinforced with triangles, made of 1/8” - 1/4'' -inch plywood, nailed and glued to the back. All wood should be seasoned, cured, or kiln-dried and should be free of knots. Cross bracing is most often done every 18 inches. With heavy bars made from 2" x4" wood, cross bracing is done every 36 to 48 inches. A Framed Panel Support is a piece of lightweight mahogany veneer plywood with a frame attached to the back to give additional reinforcement to prevent warping. Panels such as these are used to stretch canvas over. The panel is made from plywood '/s-inch thick, or '/4-inch thick for larger sizes. The frame is made of l" x 2" (milled 1" x 2" is actually ¾” x 13/4") mahogany strips with cross bracing every 16 inches. The panel is glued to the frame and sealed with a wood sealer. The advantages of this type of auxiliary support for stretched canvas is that it is strong, yet lightweight, and it allows for the easy sanding of a gessoed surface to achieve a smooth finish. It also provides support for drawing and for egg tempera paintings. The problem with this kind of rigid support is that the canvas cannot be tightened without restretching. In addition, care must be taken not to glue the canvas accidentally to the surface of the panel when sizing it or when preparing a ground. Stretcher Bars are designed so they can be assembled without being fixed in place, and the comers can be expanded after the canvas has been stretched. They should always have a raised lip at the outer edge to keep the canvas from touching the inside edge of the stretcher bars and leaving an impression. The main purpose of stretcher bars is to remove any sagging of the canvas-a recurrent problem with linen-which can occur during stretching and sizing, as well as during the application of the ground. Expanding the corners of a painted picture is not wise because small cracks can develop, which will eventually become larger, especially in older paintings. The general rule is that if a sagging painting cannot be corrected with minor adjustments, leave it alone or get help from a professional restorer. There are several types of corner designs-tongue and groove, Lebron, Muleski, and Starofix. The tongue and groove system is the style most commonly used for commercially made pine stretcher bars. They range from 5/8 to 11/16 inch in depth and 1 1/2 to 1 5/8 inches in width, and lengths from 6 to 72 inches with increments of one inch. One end of each bar is cut so that it will slide into the groove cut into the end of the other bar. The cutting remnants, which are in the shape of little triangles, are used to expand the corners by wedging them into the gaps in the inside of the joined corner after the canvas has been stretched over the bars. A heavy-duty version of these bars can sometimes be found in art supply stores or can be ordered through them. One of the best I have seen is manufactured by the Best Moulding Company and is illustrated opposite.
Two types of hardware are used to expand the corners of stretcher bars. The first type is a turnbuckle, which involves a metal link that holds together a screw on each end. The screw has an eyelet at the end so that it may be fastened to a surface. The screws have opposite threading so that when the link is turned the screws are pulled together. The Muleski stretcher bar corners, named after the designer Thomas Muleski, employ turnbuckles. The corners have a large groove in which a small aluminum plate is inserted and the eyelet turnbuckles are fastened to the inside of the corner groove. The link is exposed in the inside of the corner and when turned the corner expands along the aluminum plate. The Lebron stretcher bar system, named for the designer James Lebron, uses a Tite-Joint Fastener, which consists of a locking sleeve on one edge of a draw bolt and a tightening nut assembly on the other end. The nut assembly and the locking sleeve are embedded into each side of the corner. Dowels are placed on each side of the draw bolt, parallel to it. The corner is expanded by turning the round nut with a pin or nail, which fits into small holes made for this purpose. As the comer expands the dowel maintains the alignment of the corner. A new development in stretcher bars is the use of extruded aluminum strips with outside edges made of wood. A company called Starofix has developed what it calls a "continuous tension stretcher." A type of adjustable spring clip is used in the inside corners to keep the canvas stretched taut. They are lightweight, and so strong that cross braces are not required for lengths less than 72 inches. They are ideal for conservation work and for very large canvas works. However, they are expensive and their high price puts them out of reach for most painters. In addition, they are not readily available outside New York City. (Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987)
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