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Bank Canvases
Stretching and preparation

Somewhere during man’s intellectual evolution, between painting and carving images on stone and creating digital images on a computer, (somewhere just before the Renaissance) he discovered the luxurious support of canvas to paint on. Early masters and collectors of art appreciated the value of this rich surface and as well as its ease of transport. This was a tremendous advantage for the traveling artist, provided there was not an exceptional amount of paint build up, when a completed painting could be removed from it’s original stretcher, rolled up the same as paper and placed in a carrying tube to protect it from the elements.

“The art of painting”
Jan Vermeer

oil on canvas    1666-1673

Today this traditional surface continues to dominate a large percentage of admiration and is chosen for it’s luxurious texture, strength and lightweight.

The most common and logical inquiries about canvas examine the difference between ready stretched and stretching your own canvas.

Vermeer and His Milieu : 
 A Web of  Social History
by John Michael Montias

 

There are advantages to using both. However, there are also important considerations that should be taken about canvas stretching.

  • Stretcher brace design for strength and to prevent warping (a common problem). It’s an eminent embarrassing disappointment to find your masterpiece once completed stretched over a brace that has started to warp and twist preventing it to lay flat hanging on the wall. The major contributing factors to this problem are the use of inferior lumber and the brace design itself.
  •  Is the primer applied to the canvas before or after it has been attached to the stretcher? An important benefit to sizing and preparing a ground to raw canvas after it has been stretched is the effect sizing and primer has on canvas. Causing the cotton duck to shrink when sizing has been applied, the work surface is pulled tighter than it would be to pre- primed canvas. Linen however, also an absorbent fiber will not shrink as much as cotton.
  • There are many grades of canvas available to choose from if you stretch your own. This is a choice you may not have with ready-made pieces. Artist canvas is made from three natural natural plant fibers, cotton, flax and hemp. Because it’s an economical resource most pre-stretched canvases are almost always made from cotton. Known as “Cotton Duck” produced only for the art market it can be used for a professional grade painting as long as it’s weight no less than 12 oz per sq yard (preferably 15 oz). These are terrific supports for aqua mediums such as watercolor and acrylic.

The higher quality linen for use with professional art is manufactured extensively in Belgium, Ireland and Italy. Produced from the flax plant (Linum usitatissimum) it is  exceptionally resistant to decay and somewhat insect resistant. Hemp is equally if not stronger and is making it’s way back into the market. Flax and hemp Linens are a much stronger archival fabric and because it is more closely chemically related, are the preferred canvases for use with oil paints. Weight of linen is determined by how finely it is woven either single weave or double weave (where each thread is doubled for strength) and by number of threads per square inch. Grades of linens vary. There is a wide range of both pre- primed and raw linen available. Many distributors carry the minimum of three categories:

Heavy or Course – used primarily for murals and landscapes where the texture enhances it’s appearance.

Medium – is a general purpose canvas where strength is more important than texture. (minimum 70 threads per inch)

Fine – or Linen for work where a fine smooth surface is desired such as with portraits.( 90 or more threads per inch)

Note: if your supplier does not offer this sort of information about the linen they are selling there is a chance it may not be an acceptable grade for art.

  • Where the nature of this publication places emphasis on the proper application and the use of archive quality materials, I find it only fair to comment on the development and use of polyester fabric as stretcher painting canvas. After reading the Ottawa Conservators Report (.pdf file) excerpts from “Artists Canvases: Their History and Future” there are hopeful expectations and claims that polyester canvas may be more resistant to environmental and  biological deterioration than cotton, flax or hemp fibers. One favorable aspect is that polyester does not require a size such as RSG or PVA to protect the canvas from the degradation properties of oil paint. It is also interesting to find this report however, the statement “there is very little evidence available to quantify the effects of such contact” with cellulose textile materials. I myself question the necessity and /or documentation about protection from flax-seed oil used on flax linen canvas.

If you don’t have the time or feel you are incapable of stretching your canvas then purchasing ready stretched canvases is the safest recourse. There are many different manufacturers of quality pre-stretched canvases available from suppliers around the world. However keep in mind, not all are made equal. If you prefer to buy pre-stretched canvases at least be wise to how the ones you are using are made.

Here’s a great tool I wish was available many, many years ago . Once you have the clamps positioned on either end of a canvas the straps pull from both ends with a ratchet the locks the tension in place until you get the canvas tacked or stapled in place.  A bit pricey but a worthy investment.  

Materials 

Preparing to stretch your own canvas you will need to have the following materials:

Stretcher Bars – Each pair of equal lengths of wood stretcher splines are made to fit together to frame the canvas. Pre-made stretcher bars can be purchased or you can make your own.

If you decide to make your own, the lumber used should be strong dense and lightweight like Popular or Mahogany or Teak. If at all possible when making your own, kiln dried pieces should be avoided. Most manufacturers use kiln dried Popular for the most obvious reason, cost.

 The design should allow for tightly fitting corners with a tongue and groove joint which, resists warping. Pieces larger than 28″ should be at least 1″ thick such as Masterpiece Heavy Duty with Cross Braces. If you are serious about your work, with pieces larger than 48″ you really should consider use of the aluminum reinforced  Best Pro-Bar System shown at right.

Best Pro-Bar Stretcher Bars

Fasteners – staples or #6-1/2″ copper upholstery tacks should be used to attach the canvas to the stretcher. Copper Tacks were used previous to staples and are still a good choice due to the metal’s rust inhibiting properties. Another plus is that the canvas can be removed from it’s frame without damage and re-stretched if needed. A Heavy Duty Staple Gun is the modern tool for this job.

Canvas – either cotton Cotton Duck Canvas make the best surfaces.

Stretcher pliers– Use these pliers to assist pulling the cloth tightly over the stretcher frame.

Rabbit glue or PVA sizing – The traditional ground starts with a layer of glue sizing and then an oil primer ground is applied. Sizing aids in creating a resistance from absorption of the paints used by sealing the pours of the fabric when applied previous to a primer ground. This is a serious step especially when painting with oils since, oil paint can cause the cotton duck to deteriorate prematurely.

Scientists and conservators claim that rabbit skin glue absorbs moisture and expands and contracts in changing atmospheric conditions causing oil painting surfaces to crack. Another theory is that these cracks were caused by failed Artist technique covered in “Oil Painting” . The suggested alternative is to use for sizing an oil painting is a Neutral pH PVA (poly vinyl acetate) Adhesive diluted with distilled water or a pre-mixed version such as Gamblin PVA Sizing. Two to three coats may be required to seal and protect the canvas from oil absorption.

Acrylic Gesso – Acrylic Polymer Gessoes have replaced oil primer and is an effective ground base for both acrylic and oil base paint. Some claim that you do not need to size when using Acrylic Gesso because, it primes and fills most porous absorbent surfaces in addition to providing a protective layer and a smooth matte surface to paint on. I’m not positive about this issue since, acrylic has only been around for about half a century or so.

Acrylic paints are not the same as acrylic gesso. You should  use only acrylic gesso that has been developed specifically for artists’ use.  Be cautious of inexpensive gessoes, they may be just a relabeled version of acrylic house paint. Don’t thin acrylic gesso with only water. Use a solution of 50/50% water and acrylic matte medium. All gesso grounds can also be tinted for those who want to start off with a base tone. Gesso can be tinted Black, Brown, or Gray for special effects or to create a tonal base to start from.

There is one disadvantage of using Acrylic gesso on canvases to be painted with oils. Because it’s chemically a water base paint, Acrylic gesso requires at least three to four weeks or longer drying time before beginning a painting with oil depending on the humidity. Otherwise, any moisture left in the ground sealed between an oil painting and the canvas sizing will have difficulty escaping causing cracks and blisters long after the work is completed.

Oil Priming –To avoid any of these complications, if you are working with oils, you should always use an traditional oil base primer with such as Williamsburg Lead Oil Ground and Rublev White Lead Primer or an alkin resin binder like Gamblin Oil Painting Ground. It  is dries in less than a week and it’s more compatible for use with oil paints. Because oil paint should not be applied directly to the canvas, sizing first is always required to seal the canvas first.

Note: If desired you can also grind your own oil primer using lead white paste or titanium white and/or your choice of colors from the tube to establish the tones of your painting early. As a rule however, try to use the faster drying colors such as Ivory Black, Vermillion, Umber, Persian Blue, or Ocher for this task. Grind these colors into a pre-made medium of sun-thickened linseed oil and whiting chalk as a filler to a consistency of a paste. If too thick to apply you can thin the paste until it works like a thick paint with turpentine or Copal resin medium.  This thin coating should dry fast allowing you to build your desired ground quickly.  

Large paintbrush – I have found that  good quality 3″ or 4 ” Nylon house paint brush works best here for applying acrylic gesso. You will need a China bristle brush or a large Hake to apply an oil primer ground. Be sure to use one that’s clean and in good condition but HAS BEEN used before. The reason for this is, that sometimes a new brush will have the tendency to shed. You do not want to deal with finding brush hairs in your painting ground if you are attempting to produce a smooth texture.

Large angled palette knife – An alternate means of applying your gesso ground on canvas is to use a stiff angled palette knife with rounded edges to push the ground into the gaps of the canvas while scraping thin coats and thus leveling and smoothing the surface.

 Stretching your own canvas support

    1. After determining the size of your painting, match TWO EACH of equal length stretcher bars (i.e.: 2/24″ +  2/28″). With the equal sizes parallel to each other, join the mitered edges of  four stretcher bars together. Measure diagonally corner to corner both ways and adjust to equalize distance to make certain your stretcher is square. Adjust frame until both measurements are the same distance. Lightly  secure in  place with (ONE) 1/2 inch  brad in each corner.  Install cross braces (if used) rechecking  the square as you go and secure them in place with  brads.  
    1. Be sure you have measured and cut  piece of  canvas at least 3″ in excess around all four sides of your frame for  grip while stretching. Try as best you can to align one edge of the frame square with the weave of the canvas and the fasten it in the center of the bar. Pull the canvas tightly across to the center of the bar parallel to where you just fastened it and fasten the opposing side.
    1. Stretching evenly from side to side and working from the center outward stretch the canvas as tightly as possible fastening it about every two inches as you go. Canvas pliers are of great help here to obtain a strong grip. Continue fastening back and forth on the two parallel bars until you get about 2 inches from each corner. See figure the below (step 2) to use as a reference to the order of fastening.

Canvas Fastening Order

After you have finished stretching one set of parallel sides turn the piece 180 degrees and  repeat step two to the other two sides (see figure step 3 above). Be sure to watch for ripples or any unevenness in the canvas as you go to avoid having to repeat the process.

  1. When you reach the corners take remaining canvas, crease it, fold it back, and staple tightly in (see the figure below step 4). Cut off the excess canvas along the back edge of the stretcher with a razor knife.

Fold and Tucking Canvas Corners
 

There is another version of finishing off the edges of your canvas known as “wrap” and another way to use it with “bevel” stretchers. These techniques are used for applications where no frame is used. The stretching is done basically the same except the fastening is wrapped and folded behind the frame where the edges of the painting are painted.

Preparation 

Rabbit glue sizing 

In a sauce pan add about 2 ounces of Rabbit Skin Glue to about a quart of distilled water. While stirring, warm the solution until all of the glue is dissolved. Do not over heat or boil. Only heat the solution enough to start melting the glue and then remove it from the burner.

Let the glue stand to cool until it is in a gelatin state. This is to be certain the glue and water were thoroughly mixed.

Warm the solution up again until it thins to a paint consistency, and you are ready to apply the sizing as heavily as possible covering every inch of the canvas. Work your brush vigorously across the surface to make certain the canvas fibers absorbs the sizing. Allow to cool and thoroughly dry.

PVA glue sizing 

In a pan dilute Neutral pH PVA (poly vinyl acetate) Adhesive with distilled water to a thin paint viscosity (warm if needed to mix thoroughly) and apply the same as rabbit glue. Allow to thoroughly dry. Gamblin PVA Sizing is a pre-mixed ready to use version design specifically for this purpose.

Primer ground 

Next you will need to apply the Gesso/primer. At this step many artists also apply a few coats of Acrylic Gesso to ready – stretched canvases to obtain their desired surface ground previous to painting. Apply using a cross hatched pattern or apply brushing across the canvas with one coat and then up and down the canvas the next. Since it will be difficult at first to apply evenly, you will most likely have to apply  three to five coats, lightly sanding or scraping between each coat.

If you decide to apply your ground with a palette knife which is best when painting with oils, it is applied about the same except as you are passing across the canvas you are pressing firmly (cautiously to prevent gouging it) filling the crevices of the canvas removing the excess gesso as you go.

*Drying time will vary and it may take a few days until you obtain your desired surface. If painting oil over an oil base primer you can begin painting as soon as it is dry to touch. The same rule would apply to an acrylic painting over an acrylic primer. However make certain to allow adequate total dry time of  at least 6 weeks if painting oil over acrylic gesso.

“We never really know what stupidity is until we have experimented on ourselves.”…….Paul Gauguin

 

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