An Essential Guide to Primed Artists' Canvas
Today's consumer is confronted with a myriad of woven materials, all claiming to be "artists' canvas".
Unfortunately there are no standards to control such claims, and many of these products are good for little else than temporary decorations.
This guide is designed to unravel the hype and give the artist and art student the facts to enable them to choose a suitable canvas for their needs.
The canvas, and its priming, is the foundation of a painting. A wise tradesman would not contemplate building a house on inferior, unstable foundations; likewise an artist should be just as selective about the canvas they use.
There is no evidence that artists of the past were more affluent than those of the present, but there is plenty of proof that they never tried to effect economies at the expense of quality. The use of second-grade materials and inferior methods in creative painting is a mid-twentieth-century phenomenon.
From The Artist's Handbook of Materials and Techniques by Ralph Mayer
WHAT IS CANVAS?
Canvas is a generic term used for cloth woven from relatively coarse fibre. In painting the term canvas usually means a coated (primed) fabric, ready to use. Practically every type of woven textile has been utilized at some time for paintings, with linen, cotton, hemp and jute being the most common.
CHOOSING A CANVAS
In selecting a canvas the artist must consider two important factors: the support (woven cloth) and the ground (gesso or priming). These factors are critical to the soundness and stability of the final painting. The technical success or failure of a painting is dependent on the correct choice of canvas and the method of application of permanent artist colours and mediums.
This guide will only examine prepared canvas, particularly, acrylic gesso primed cotton duck, which is widely available but often the most unsuitable for artist use.
Strength and stability of the woven fabric support is essential for permanent painting. This is because over time the support will be subjected to movement and stress caused by many factors, including temperature and humidity changes, stretching and/or restretching of the artwork and general handling.
|The critical attributes for a strong, stable support are:||
12oz Cotton duck note tight,
|1.||Warp and weft threads should be of equal weight and strength. They should also be of the same material.|
|2.||Close and tightly woven yarn with a square (1:1 or 2:2) weave, which provides dimensional stability.|
|3.||Loomstate canvas ie untreated with domestic or industrial conditioners and bleaches.|
Cotton as a support
By far the most widely used support for leisure and hobby artists, and art students, is cotton duck. Good quality cotton duck can provide a suitable support for even professional artists, albeit not as strong or stable as quality linens. This is because cotton fibres are short and flat (only 4 to 5cm long) whereas linen fibres are round and can range from 25 to 90cm in length.
Unfortunately most of the cotton duck widely available is price driven, and not suitable for artistic use.
14oz and 12oz Cotton
These are the best quality cottons, and when woven with the 3 critical attributes described previously, provide a very good support for artwork. These cottons have a more uniform texture than linens, and can be preferred by some artists for certain techniques. Until recently good quality 12 and 14oz cottons were hard to obtain and quite expensive. However, Art Spectrum now sources excellent and well priced canvas in both weights.
A tightly woven 10oz loomstate cotton can have two of the three critical attributes for an artists' support. Most of the 10oz cotton available is a 2:1 weave - this means the fabric is twice as strong in one direction as the other. Thus it does not offer a truly stable support. A well woven 10oz cotton duck can be used if financial constraints allow nothing better, or for small works where there is likely to be relatively less stress and potential for movement.
Because of low price and ready availability, these weights are frequently used, particularly in the pre-stretched canvas market. Cottons of this weight and below are of scenic quality only (ie suitable for making theatre sets, banners and other short lived projects) and are not suitable for serious artwork. They invariably have quite a loose 2:1 weave, with warp and weft threads of different weights and thickness. To stiffen and increase weight, manufacturers often add waste recovered from the processing of the cotton bolls back into the woven fabric as a filler. Also many of these 7-8oz cottons are bleached which further weakens the fibres. Bleached canvas is whiter than the creamy colour of loomstate cotton. Cottons of this weight are too weak and unstable to properly support a paint film and should be avoided wherever possible.
8oz Cotton duck showing loose, 2:1 weave
Blends of fibre (ie cotton/polyster or cotton/linen) should be avoided as the final product is usually unstable due to the different weights, strengths and characteristics of the two yarns. They are only suitable if the blend is in the thread, and exists in equal weight ratio in the warp and weft.
For the purposes of this guide only factory applied acrylic gesso grounds will be considered, although the same critical characteristics apply for home or studio applied gesso. The ground (priming) performs these principal functions:
|1.||It isolates the support (canvas) from potentially damaging ingredients in the paint. For example, oil seeping into the fibres of the canvas can cause their disintegration.|
|2.||The ground provides a surface that accepts the paint and allows adequate adhesion. It must have enough tooth to accept the paint, and a degree of absorbency. But too much absorbency can soak up the binder (oil) from the paint leaving a brittle film liable to crack. A non-absorbent ground can produce a paint film that is liable to peel off.|
In transparent and semi-transparent painting techniques the ground enhances colours by providing a white, reflective background.
Choosing a suitable ground
It is very difficult to tell whether a ground is suitable for artistic use from appearance alone. A canvas primed with household acrylic undercoat may look fine, yet the manufacturers of even the best quality house paints specify a life of less than 10 years! The foundation of a painting needs the capability to last generations, not 10 years! And many of the cheap canvas products available today use priming inferior to even that!
Things to look for in labeling are firstly the use of genuine Titanium pigment and secondly that a quality acrylic polymer has been used as the binder. A brand that you know and trust, purchased from a reputable art supplier, can also be a guide to quality. The best quality is always double (or even triple) primed, but this is not always stated on the label.
A simple test for a canvas is to pour a small amount of linseed oil onto the primed surface and leave it for several days (although sometimes a few hours is enough). If the oil soaks through the priming and discolours the canvas underneath (see pic on right) then it is not suitable for artistic use.
Inspect the back of a pre-primed canvas for quality and closeness of the weave. Cheap, fragile open weave canvases sometimes show the priming, which in effect is holding the canvas together (a sign of poor quality).
Clean your canvas before use
An often overlooked, but essential step in producing a lasting work of art is ensuring the canvas is clean of any dirt, grease or factory residues. One can never be sure of who or what has come into contact with the surface, even if it is wrapped. Cleaning is quick and easy, but necessary. The most effective way is to moisten a clean rag or sponge with either Art Spectrum Medium No.1 or Reduced Odour Lean Medium and thoroughly wipe the entire surface of the canvas. This has the dual effect of the solvent component of the medium cleaning and removing any dirt or grease, and the oil component "keying" into the gesso to provide a more receptive surface for the subsequent layers of oil paint. (Note: if you plan to paint with acrylic, you should use solvent only).
Linen is clearly the best natural fibre for artists' canvas. Sourced from the flax plant (from which the seeds are harvested to provide linseed oil) linen fibres are stronger than any other natural fibre. In length they range from 25-90cm and are round, not flat like cotton. This shape, as well as providing extra strength, produces an irregular and far more interesting texture which is ideal for painting because of the sense of depth it gives to the surface. If linen is woven in accordance with the three key principles described previously, it produces a stronger and more stable support than any other fabric.
The best linens in the world come from Belgium, and a few manufacturers there also produce some superb hand sized primed products for artists use.
Art Spectrum is proud to be the exclusive Australian agents for the Claessens range of Belgium Linens, which includes a wide variety of weaves from very coarse to very fine, and both universal (acrylic gesso) priming as well as traditional oil priming.
Whilst linen may be expensive compared to cotton, the difference in an average sized painting (16" x 20") is probably only $10-$20, depending on type. When the total cost of a painting, including framing, is taken into account this is a relatively small extra price to pay to use the best.
HOW TO PREPARE CANVASSES FOR OIL AND ACRYLIC PAINTING
Methods of Canvas Preparation
1. Using glue size and oil primer
2. Using Art Spectrum Oil Prime (without glue size)
3. Using Art Spectrum Artists’ Acrylic Gesso (NB Canvas prepared for acrylic painting should only be primed by applying acrylic gesso to the canvas. Glue size should not be used under acrylic gesso.)
1. Using glue size and oil prime
Glue sizing and oil priming are the time tested traditional methods of preparing canvas for oil painting.
Glue sizing (with Art Spectrum Rabbit Skin Glue)
A size is made by dissolving 8 level tablespoons of rabbit skin glue in 1 litre of cold water. Soak until all the water has been absorbed by the glue to a porridge consistency (for 1 hour or overnight).
Stir and heat gently in a double boiler (never boil the glue as this weakens it). Open your windows if the smell of hot glue is unpleasant. Always use a clean container and do not make more than you can use in one session. Make a fresh batch for each day’s work.
Apply when still slightly warm with a 5-10 cm stiff brush or sponge onto the canvas. If a smooth surface is required, palette knife the size. When applying the glue size to canvas, do not press so hard as to make the canvas touch the timber support or ‘strike-through’ will result and the canvas will be glued onto the stretcher. To avoid this, use one hand to slightly raise the canvas (from the back) away from the timber support. Do not size directly over areas that your hand is supporting, otherwise strike-through will occur there. Sizing the edges will prevent unraveling.
Keep the canvas flat while wet and under tension. If necessary, lay the canvas face up on the floor (or any flat surface) and weigh down the corners. The canvas will shrink more with the glue sizing than with acrylic gesso. When dry it may be sanded lightly with sandpaper and then resized. The second coat of size should not be sanded. Size is not intended to form a continuous level film.
Glue size can also be applied cold (in a jelly state). Using a spatula, work the glue in well, smoothing the excess off the canvas. This is particularly effective for open weave canvasses. Size acts as a penetrating liquid to fill the pores of the canvas and isolate the fabric from strike-through of subsequent applications of primer and oil paint.
For glue sizing paper, adapt the recipe to make a weaker mix, using 5 to 6 tablespoons of rabbit skin glue to 1 litre of water.
Oil Primer is a mixture of Art Spectrum Titanium or Zinc White oil paint (although any Art Spectrum oil colour can be considered) and Oil Medium No 1.
Thin paint to a brushing consistency with Medium No 1 and apply in thin coats with a broad brush. Finish off by gliding a palette knife over the surface. Leave for 24 hours between coats and leave for at least 7 days before using the canvas (this may vary with the climate in your area). Aging primed canvasses for 6-12 months was widely practiced by the old masters and is still considered best practice.
2. Using Art Spectrum Oil Prime (without glue size)
One of the best priming methods is with Art Spectrum Oil Prime – use direct from the tin. No glue sizing is required and there is no need for multiple coats. Apply as you would an acrylic gesso. You can thin it out with water. Art Spectrum Oil Prime can be painted over as soon as the moisture has evaporated, usually the next day. It contains just the right amount of linseed oil, which provides chemical cross-linking and excellent adhesion.
Art Spectrum Oil Prime is available in 500 ml, 1 Litre and 4 Litre containers.
3. Using Art Spectrum Artists’ Acrylic Gesso (without glue size)
In comparison to oil priming, acrylic is not as time tested, but it has proven to be a very advantageous and promising primer for both acrylic and oil-painting. Art Spectrum has two grades of primer – Artists’ Acrylic Gesso, which is best for oil painting, and Low Cost Gesso, for acrylics.
Art Spectrum Artists’ Acrylic Gesso has been carefully formulated by professional paint chemists to provide a permanent ground for oil and acrylic painting. Artists’ Gesso will dry to a brilliant white in a few hours, providing an absorbent, permanently flexible, waterproof, non-yellowing ground. It is suitable for use on most clean, non-greasy surfaces including canvas, timber, masonry, boards, masonite, and appropriate papers.
Gesso should be applied directly to the raw canvas or other support. Smooth supports, such as masonite, should be lightly sanded first to provide tooth for the gesso to bond securely onto the surface. Preliminary sealing of the canvas is usually not required.
Artists using wash techniques, and wishing to prevent colours staining through the back of the canvas, can seal the raw canvas with a solution of 50% water and 50% acrylic medium. Moistening the canvas (by lightly spraying with water) before gessoing will not only tighten the canvas, but will also make the application of gesso easier. For one coat application, use gesso straight from the container and work the gesso well into the canvas. Gesso can be applied by brush, spatula or sponge for different textural finishes.
Priming – first coat
Stir gesso well before use. Wet the brush before dipping it into the gesso. Start at the centre and work out evenly towards the edges of the canvas, working well into the fibre, thoroughly covering one area at a time. Brush gesso in one direction and then across in the other direction. At the start of gessoing, gentle pressure with your hand at the back of the canvas will ensure that your canvas remains clear of the stretcher and bracing during priming, to avoid strike-through. Do not gesso over areas that your hand is directly supporting, otherwise strike-through will occur there. Seal container firmly after use and wash all equipment in water immediately.
Priming – second coat
Once dry, the first coat may be lightly sanded with a fine sandpaper, if desired, before the second coat. This will give a smoother finish. Do not sand the final coat. When sanding near the braces or stretcher arms, gently raise the canvas from behind to avoid sanding an impression of the timber support. For coloured grounds, the gesso can be tinted with Art Spectrum Liquid Spectrum over the dried gesso. For painting in oils, some artists give the dried gesso a coating of Art Spectrum Medium 1 or Art Spectrum Low Odour Lean Medium to seal the ground and reduce the absorbency of the gesso. Oil colours may be painted over with Medium No 1 or Lean Medium, wet or dry.
Art Spectrum Artists’ Acrylic Gesso is a compound of Titanium Dioxide, Calcite and Mica in an acrylic polymer latex base.
It is available in 250 ml, 500 ml, 1 Litre and 4 Litre containers.
Art Spectrum Low Cost Gesso is a compound of Titanium Dioxide, Calcite and Mica in a vynol latex / carboxy alkyl cellulose binder.
It is available in 1 Litre and 4 Litre containers.
For information about your nearest supplier contact Art Spectrum.