GB2131356A - Frames for tensioning canvases - Google Patents

Abstract

An artist's canvas is stretched prior to painting by being laid over and secured to a flat expansible inner frame 10 which nests within a rigid outer straining frame 20. Each segment 12 of the expansible inner frame is directly coupled to a corresponding element 22 of the rigid outer frame by a screw 24 which is accessible from outside the periphery of the rigid outer frame. The whole assembly is planar and can be mounted in a normal picture frame 30. Flat surfaces are formed around the inner periphery of the outer frame for the mounting of detachable rigid panels on the front and the back of the complete assembly for secure protection during transport. <IMAGE>

Description

SPECIFICATION Improvements in frames for tensioning canvases This invention relates to frames for tensioning canvases, especially (although not exclusively) canvases of the kind commonly used by artists. In this specification the term "canvas" is to be understood as embracing not only hessian or like jute-derived materials but also other flexible sheetings whether woven from natural or synthetic fibres or non-woven and having sufficient tensile strength to permit their being stretched taut over a flat working area such as the surface on which a painting or drawing is to be executed. The term "a canvas" means a piece of such material of the appropriate size.

Background to the invention When an artist wishes to paint a picture on a canvas he normally attaches it securely to a wooden tensioning or "stretcher" frame so constructed as to be expansible in two directions at right angles in the plane of the painting surface. Assuming that the frame is of the conventional rectangular shape, all four corners are formed by loose or freely movable mortise and tenon joints into each of which it has hitherto been customary to drive a wedge which forces apart the two segments or bars of the frame which are expansibly interconnected at that corner.

When all four wedges have been driven in, the segments or bars making up the stretcher frame are spread further apart, and the canvas secured thereto is tensioned in two directions at right angles.

This conventional system has certain disadvantages: (1) the necessity of using wedges to spread the segments or bars of the tensioning frame has limited the minimum size of canvas to about 8 inches square. The present invention enables the minimum size to be reduced to about 2 inches square; (2) the act of hammering a wedge into an expansible corner can cause damage (especially if a picture has already been painted on the canvas in which case the paint layer itself can be cracked or flaked) either by a direct badly-aimed blow on the back of the canvas or the shock of the hammer blows on the wedges; (3) wooden wedges tend to shrink in time and to fall out, sometimes becoming trapped between the canvas and another segment or bar of the stretcher frame leading to fracture of the paint layer;; (4) a long canvas tends to sag in the centre, and a "cross-frame" stretcher has to be provided. In time, this results in cracking of the paint along two parallel lines coinciding with the edges of the cross-frame stretcher; (5) when an artists' canvas is placed on an easel, the clamping action of the easel causes the canvas to slacken in the centre.

The present invention aims, among otherthings, at eliminating or reducing the above disadvantages.

It also seeks to provide certain positive advantages, including the following: (a) as a result of the reduction in the viable minimum size of canvas which can be stretched, paintings smaller than 8 inches square can be restored using the technique of relining by the museum-approved "wax/resin vacuum" method; (b) protection of the back of the canvas - which is highly vulnerable to impact, accounting for a high proportion of the damage to oil paintings - by fixing a readily detachable sturdy backboard or panel to the frame; (c) the possibility of retensioning a painted canvas without the necessity for its removal from the frame, or even from the wall on which it is hanging; (d) the prevention of bodily lateral movement of a painted canvas in the frame, which causes scuffing of the margins of the painting;; (e) greater ease of protection of a painting for transport and shipping whilst providing ready ac cess for customs inspection and reduced weight of packaging; (f) the facility for a wide choice of alternative surface colours and decorative patterns on the frame using a single stock moulding.

Precis of the invention With these and other objects in view, the invention provides a canvas tensioning system which consists of open outer and inner frames ofsubstantaillythe same overall shape which are nested in the same plane with clearance between them all round the periphery of the inner frame, each component or segment of the inner frame being directly coupled to a corresponding part of the outer frame by a manually operable tensioning device. The several components or segments of the inner frame are interconnected for mutual displacement in the com mon plane of the frames by expansible joints permitting adjustment of the gap between the corresponding components of the inner and outer frames so that the overall size of the inner frame can be increased and thereby stretch the canvas.The several components of the outer frame, on the other hand, are rigidly interconnected so as to provide abutments for the tensioning devices.

Preferably, the tensioning device is a screw whose axis lies in the common plane of the frames.

Ideally, each tensioning screw is accessible from the outer periphery of the outer frame.

Advantageously, the inner frame is made of wood, and the tensioning screws are wood screws whose threads are engaged in the respective components or segments of the frame.

Conveniently, the interconnection between meet ing components or segments of the inner frame is a mortise and tenon, the tenon being free to slide within the mortise.

Brief description of the drawings The invention will now be described, by way of illustration only thereof, with reference to the accompanying drawings in which: Figure 1 is a part-sectional plan view of an assembly of coplanar inner and outer frames for applying tension to a canvas (not shown); Figure 2 is a scrap section on the line ll-ll in Figure 1; Figure 3 is an end elevation of the assembly in Figure 1 seen in the direction of the arrow Ill in Figure 1; Figure 4 is a section on the line IV-IV in Figure 1 showing a canvas ready for tensioning, and certain detail modifications not shown in Figures 1 - 3, and Figure 5 is a view similar to Figure 1 of an oval frame assembly.

Detailed description of the drawings Referring first to Figures 1 - 3, a rectangular open inner expansible frame 10 to which the canvas to be tensioned can be secured consists of four straight rigid bars 12 which constitute the components or segments of the frame. At each corner of the frame, the meeting bars 12 are interconnected by a mortise and tenon joint in which the tenon 14 is a snug sliding fit within a mortise 16. The inner frame 10 is expansible in its own plane according to the degree of insertion of each tenon 14 into its coacting mortise 16.

The inner frame 10 lies in the same plane as an outer rigid abutment or straining frame 20 which is also rectangular and has approximately the same proportions as but is largerthan the expansible inner frame, so that up to its limit of expansion the inner frame 10 nests within the outer rigid frame 20. The latter has four rigidly interconnected bars 22 which provide abutments for a number of tensioning screws 24 whose axes lie in the mean common plane of the inner and outer frames 10,20. In Figure 1, two tensioning screws are shown in full lines, the remainer are indicated by their respective centrelines.The length of the tensioning screws 24 is sufficient to leave enough thread on each screw operatively engaged with the respective bar 12 when all the gaps between bars at the corners are closed to ensure that the bars can begin to be separated by tightening the screws uniformly all round the periphery of the outer frame 20. As this action is performed the tension in a canvas which has been suitably anchored to the bars 12 (see, for example, Figure 4 described below) will progressively increase in two directions at right angles. When the desired tension is reached, the screws 24 lock the inner frame in its expanded condition.

From the foregoing description it will be evident that the bars 22 of the outer frame 20 must be stiff enough to resist any significant deflection under applied tension. Whilst wood is likely to be the most convenient material for both frames, it is to be understood that at least the outer frame 20 can be made of metal or a suitably strong plastics material including a metal-reinforced plastics. Furthermore, although the inner frame 10 may be made of wood, the wood screws 24 may be replaced by metalthread screws working in nuts or threaded bushes held captive in the bars 12.Alternatively again, the screws 24 may be reversed, their head ends being rigidly anchored in the bars 12 and their threaded ends being engaged with rotatable threaded nuts or bushes held captive in the outer frame bars 22 and provided with suitable formations for engagement by a key or screwdriver as in the case of the countersunk wood screws 24 already described above.

The location of the coaxial holes in both frames 10, 20 in which the tensioning screws 24 work, both as regards the pitch of their axes measured lengthwise of the bars 12,22 and the centralisation of their axes with resepct to the thickness of the bars 12 on the inner frame 10, is preferably chosen so that the inner frame 10 can be turned overfor painting by the artist and reversed when the painting has been completed. In Figures 1 - 3, where the bars 12,22 are shown with a purely rectangular cross- section this facility is of minor importance, but where, as in Figure 4, the cross-sectional shape of the bars 22 of the outer frame 20 is asymmetrical, it is of great advantage in allowing the entire flat surface of the tensioned canvas to be accessible.Moreover, the back of the outer frame 20 provides a convenient place for the artist to rest his mahl-stick for steadying his brush hand. Hitherto, the working end of the mahl stick has had to be rested on a part of the canvas which has not yet been painted or on which the paint has already dried, with the attendant risk of damage. If desired, the back surface 22a (Figure 3) of the bars 22 can be enlarged, as by a flange or by adopting a tapering shape for the cross-section of the bars 22, in order to increase the area of the back surface 22a available for resting the working end of a mahl-stick.

It is to be noted that the cross-sectional shape of the bars 12 of the expansible inner frame 10 is preferably not rectangular, as shown in Figures 2 and 3, but tapered or relieved, at least on the top face as seen at 12a in Figure 4. This avoids the risk of the formation, over a period, of a line on the painting where the back of the canvas makes contact with the inner edge of each bar 12. However, in some cases, the problem can be overcome by the use of a rounded moulding (not shown) which can be stuck to the outer edge of each bar 12 to simulate the "nose" or shoulder 12b in Figure 4.

Referring now to Figure 4, various detail modifications of the basic simple design illustrated in Figures 1 - 3 are shown. The relief 1 2a of at least the upper surface of each bar 12 has already been mentioned, the cross-section of each bar being shown symmetrical in this respect. This can be of advantage where the expansible inner tensioning frame 10 is of wood and is re-used more than once, as will now be described. The canvas 18 to be tensioned is wrapped around each wooden bar 12 and anchored by means of canvas tacks 18 driven into the underside. When the tack holes become too numerous, or if the wood begins to split, the frame 10 can be turned over and the undamaged former upper surface of each bar 12 is made available to receive canvas tacks.

Figure 5 illustrates the application of the present invention to an oval canvas. Similar parts carry the same reference numerals as in Figures 1 - 4. Both the inner tensioning and outer straining frames 10,20 are oval and are proportional to each other. In Figure 5, the inner frame 10 has has six bars or segments 12, the small radius ends defined by single seg ments, but any other number and distribution of segments can be adopted according to preference.

Each bar or segment 12 is also shown directly connected to the adjacent corresponding bar or zone 22 of the outer straining frame 20 by a pair of tension screws 24, and all the bars or segments 12 are interconnected in similar manner to those in Figures 1 - 4 by sliding mortise and tenon joints 14, 16.

In both embodiments of the invention illustrated in Figures 4 and 5 of the drawings, the bars 22 of the outer or straining frame 10 are deeper than the bars 12 of the inner or stretcher frame 10, and their inward faces are rebated to form a lip 23 which masks the outer edges of the bars 12 and the wrap-over of the canvas 18. The top face of each bar 22 is also recessed at 25 to carry a coloured or decorative strip as indicated at 26. This is preferably easily removable so that the appearance of whole picture can be modified to suit the decor of the room in which it is hung.

The rigidity of the outer or straining frame 20 enables the front and back faces of the tensioned canvas to be strongly protected from damage by providing an anchorage for front and back protective panels 27. These panels can be readily removed by undoing a few accessible screws 29. This enables customs inspection to be expedited as well as providing stout but lightweight packing for transport.

Instead of screws 24, toggles or eccentric strainers can be used for expanding the inner frame 10 relative to the outer or straining frame 20. Alternatively again, each screw 24 can be replaced by a tensioning wire or cord of the same axis and having one end anchored to one frame and its other end fixed to a tensioner such as a "capstan" device on the other frame. Two such wires or cords acting on the same inner frame segment can be oppositely connected to a common tensioner so as to equalise the force on the segment 12 and to substantially neutralise the resultant lateral forces on the tensioner.

The inner and outer frames 10,20 can be mounted as a unit in a conventional picture frame 30 by means of angle brackets 32 screwed to the outer periphery of the straining frame 20 and to the back surface of the picture frame 30. Suspension hooks 34 for the conventional hanging of the framed painting on a wall can be of a size such that they do not protrude beyond the plane of the stretcher assembly 10, 20 so that paintings mounted according to the present invention can be stacked in their frames without the risk that a painting will be damaged by the projecting suspension hook on the frame of a painting placed on top or in front in the stack.

Although in the foregoing description it has been assumed that the frame assembly 10, 20 will be fitted into a normal picture frame 30, it is to be understood that the outer or straining frame 20 may be combined with a decorative moulding in a unitary component the back face of which is preferably rebated so as to expose the heads of the tensioning screws 24 and also to recess the suspension hooks or eyes 34 as shown in Figure 4. Such a combination of frame 20 and moulding serves to strengthen the outer or straining frame.

The method of securing a canvas on the inner or stretcher frame 10 is optional. Thus, the latter may be provided with sharp-pointed hooks, or the canvas itself may be cross-laced at the back of the frame 10, or held in place by a draw-cord, in known manner.

After the canvas has been tensioned, a permanent back protective sheet or panel 27a (Figure 4 can be secured to the back of the bars 12.

Claims (12)

1. Means for tensioning a canvas comprising a pair of open coplanar frames one of a size and shape to fit with clearance within the other, the outer frame being rigid and the inner frame being expansible and adpated for the securing thereto of the canvas to be tensioned and consisting of a plurality of segments interconnected for mutual relative displacement in the common plane towards and away from an adjacent part of the rigid outer frame, and manually operable tensioning means for adjusting the gap between each segment and the corresponding part of the rigid outer frame.

2. Means according to claim 1 wherein the tensioning means is a screw connecting each segment to the corresponding part of the outer frame.

3. Means according to claim 2 wherein each screw is accessible for adjustment from the external periphery of the outer frame.

4. Means according to claim 1,2 or 3 wherein at least the inner frame is made or wood and the tensioning means consists of wood screws threaded portions work therein.

5. Means according to any preceding claim wherein the interconnection between segments of the inner frame is constituted by a mortise and tenon, the tenon being free to slide in the mortise.

6. Means according to any preceding claim wherein both frames are indentical polygonal shape.

7. Means according to claim 6 wherein the frames are rectangular.

8. Means according to claims 1 - 5 wherein both frames are of directly proportional oval shape.

9. Means according to any preceding claim wherein the outer or straining frame is integral is integral with a conventional picture frame.

10. Means according to any preceding claim wherein the outer of straining frame has flat surfaces adjacent the inner expansible frame on its front or upper and back or lower sides for mounting of flat protective panels which totally cover the inner expansible frame and any canvas mounted thereon.

11. The combination with a canvas stretching frame assembly according to any of claims 1 - 9 of a rigid protective panel detachably secured to the front or upper surface of the outer or straining frame or to the back or lower surface thereof, or both.

12. Meansfortensioning a canvassubstantially as hereinbefore described with reference to the accompanying drawings.