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.
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.