Stretching, Sizing and Priming

 

A Discourse on the Preparation and Use of Rabbit Skin Glue Sizing and Egg-oil Emulsion Primer on Stretched Canvas

 

There are many different painting supports: cotton duct canvas, linen canvas, board, paper, panel, etc.. The individual has to determine which support and ground preparation suits the idea and method of working. It is important to be familiar with as many materials and methods as possible, as one support or ground may suit an idea better than another. Within a particular method, one can modify the process to get a desired result. I am going to outline how I prepare a linen canvas with rabbit skin glue size and egg-oil emulsion primer.

 

I was introduced to this method by Andrew Pankhurst in his affiliate Life Painting course, autumn 1998 at the Slade School of Fine Art, University College London. I continued to learn more from discussions with Euan Uglow, Norman Norris and Jo Volley. Practical experience using this technique was gained by using it for the preparation of most of my supports as well giving demonstrations and teaching the method to the Slade Summer School Master Life Painting Class and Life Painting courses.

My knowledge of support preparation extends beyond size and egg-oil emulsion primer owing to past usage of other materials and attendance at lectures and workshops given by Tim Green, conservator for the Tate Gallery and Ian Rowlands Methods and Materials tutor of Slade Summer School.

 

Guidelines for Stretching Linen Canvas and the Preparation and Use of Rabbit Skin Glue Size and Egg-oil Emulsion Ground.

 

Assembling the Stretcher Bars:

1.    Check all four bars for the correct dimensions

a.               There is a front and back. The bevelled side with lip is the front. This side faces the linen.

b.               Make sure that all the bevelled edges are on the same side.

2.    Attach all four stretchers together with an equal gap in the Determine dimensions of the canvas

3.    Make or buy stretcher bars corners.

a.               Move from corner to corner, closing the gap. Do not close the gap completely at any one corner before attending to the rest.

b.               After the gaps in the corners are closed. Check that the stretcher is square by using a tape measure or straight edge to measure the diagonal. The diagonals MUST be equal. It is essential that the stretchers are square. If not, the canvas surface will ripple. A wavy surface is unacceptable.

c.                Do not be discouraged if you have to fiddle for a while. Getting a square canvas is not always easy. But is definitely worth the effort.

 

Attaching the Linen:

1.    Cut the linen large enough to fold over edges and around back of the stretcher bars (approx. 2-3 inches depending on thickness of stretcher bars)

a.    The weave of linen is flexible in one direction and less flexible in another.

b.   If possible, cut the linen so the flexible weave is the larger dimension of the canvas.

2.    Attach the linen LOOSELY to the back of stretcher bars using a staple gun,

a.    Attach the linen with one staple in the centre of all four stretchers

b.   Continue with one staple on either side of the initial staple, tacking all four stretchers before starting to add another two staples on the same stretcher bar.

c.    Gently pull corners to remove any bunched-up linen from sides of stretcher bars. The linen should be smooth along the sides of the canvas.

d.   When adding staples, alternate sides in cross pattern. This creates an even tension on the linen.

e.    Rotate outward towards the corners in a cross pattern, space staples equally apart, and leave approximately two-three inches before the corner on each side.

3.    Corners. This is a similar process to making hospital bed corners.

a.    Stand the canvas on its side, facing the front of the canvas towards you.

b.   Wrap the side bit of linen around to back,

c.    Tuck middle bulky bit into a triangle shape between the edge of stretcher and the top bit of linen, gently pulling and folding the top bit of linen around the back. The fold should be flush with the edge of the stretcher. On the top side of the stretcher, there will be a triangle shape where several layers from the tuck overlap. It is important to get the multiple layers of fabric to lie flat. Attach three staples on the back of the corner to hold the folded linen in place. Making clean neat corners takes patience and repetition.

4.    The linen should be loosely attached to the stretcher bars. Do not be concerned if there are wrinkles in the linen. Both the sagging and wrinkles will be removed during the sizing process.

 

Rabbit Skin Glue Size:

Materials: rabbit skin glue granules, water, jar, tea-strainer

 

1.    Allow glue granules to soak overnight in COLD water.

2.    Drain the expanded granules

3.    Dilute one part expanded granules to 15 parts water. This is an approximate ratio. (Use the test explained in step 5 to determine whether the glue is diluted to the correct strength.)

4.    Using a double boiler, gently heat the soaked granules and water mixture. DO NOT BOIL or bring glue mixture above blood (body) temperature.

5.    After the granules have melted, cool. A fridge speeds up the testing process. It is important that the size is not too strong. It is better to use a weaker size than a stronger size. After size is cooled, run a finger across surface -- the glue should crumble easily at touch. If the glue does not solidify add more soaked granules. If the glue does not break easily add more water. Repeat process until glue crumbles easily at touch.

6.    Throughout the application, remember to keep the size at blood temperature.

7.    Using a clean varnish brush, apply the warm size in parallel strokes to the edges of the canvas.

a.    It is best to use one brush for sizing and a different one for priming.

b.   Do not overlap strokes or go over an area that has already been sized.

c.    Allow the size to run off the brush and sit on the surface of the linen.

d.   Continue to check the temperature of the size. It is important to keep it at constant temperature.

e.    Wait for the first coat to dry. Do not attempt to speed up the drying process. Linen is a temperature sensitive fabric and will sag or contract depending on humidity and temperature.

f.     Size takes approximately six hours to dry. Save the remaining size in a cool place. It should keep for approximately three days before spoiling.

8.    After each coat of size, run a blunt round palette knife around the inside of the canvas, between the linen and the stretcher bars. This frees the linen from the wood in areas where the glue has soaked though and dried. It is important to look at the front of the canvas when doing this. It is easy to put a palette knife through the edge of a canvas.

9.    Apply the second coat of size in the perpendicular direction to the first coat. Allow to dry. Again free the linen from the stretchers using a palette knife. Save remaining size for egg-emulsion primer.

 

Egg-oil Emulsion Primer:

Materials: 1 egg, cold-pressed linseed oil, water, titanium white pigment, diluted size mixture, jar, marble or glass slab, grinding muller or large palette knife, bowl

 

1.     Break egg into jar, shake, mark level on jar

2.     Double level with cold-pressed linseed oil, shake, mark level on jar

3.     Double level with water, shake. Now it is emulsion.

4.     Spoon out titanium white pigment into a small mound (size of a golf ball) on glass slab. (It is easier to mix small amounts than large amounts.) make a well in the centre

5.     Pour emulsion into the well. Mix in emulsion to create a paste.

6.     Slowly add more emulsion until the mixture is like double cream.

7.     Transfer to bowl and add more emulsion until the mixture is like single cream.

8.     Warm size. Remember to keep it at blood temperature, add size until the mixture resembles milk. Keep at blood temperature. Now it is primer.

9.     Before applying the primer, put card between the stretcher bars and linen. This prevents the stretcher bars from indenting the linen during the priming process

10. Using a stiff bristle brush (at least 2 wide), scrub the primer into the linen, making sure to cover the entire canvas including edges. It is best to apply multiple thin coats than one thick coat.

11. Allow to dry. If applied thinly, primer should dry in approximately two hours.

12. Sand between coats with fine sand paper

13. Repeat, up to four coats, or until satisfied with the surface. If the coats are applied thinly, four-six can be applied in one day. The aim is to fill all the pinholes between the weave of the linen. Depending on the quality of the linen, filling all the pinholes can be nearly impossible. Do not be afraid to scrub intensely, the linen can take the abuse.