Over the years I have been asked numerous times what the difference is between primer, gesso, size, ground and tooth ... and whether it is possible to paint directly onto an unprimed canvas.
Yes, it's definitely possible.... however, this leads to certain "challenges" including how the paint moves / behaves on your canvas as well as the chemical effect it will have on the cloth.
I've also had artists whose stretched canvases lose tension and become 'wobbly' after the application of PVA to their already primed canvas or where crossbars have actually snapped as a result of applying a water-based medium to the untreated, unprimed side of stretched cloth...
So, herewith my (broad) attempt to help make some sense of it all.
With acrylic paint - untreated canvas fibers may repel water, making "paint beads" and causing the paint not to flow
With oil paint - untreated canvas will soak up the oil resulting in crumbly paint, surrounded by halos of oil.
Weave could become more obvious than desired.
Discolouration (In the case of oil, yellowing, or in the case of acrylics, SID / substance induced discolouration - where impurities from the cloth are deposited into the paint through osmosis, resulting in a typically amber coloration)
Rotting (and subsequently smelling)
Delamination / Flaking / Cracking
Moisture in your medium can cause an unprimed, stretched canvas to shrink on drying which could in extreme cases result in your cross- / stretcher bars snapping!
Acrylic primer / PVA applied to a pre-primed stretched canvas, may result in a loss of tension and will need to be re-pulled before painting.
Primer, even the highest quality, has a limit. Turpentine is designed to corrode paint. Use too much and it will eat through any primer, dragging water / oil with it into the cloth.
(use ONLY the most refined, distilled artist's white spirit, like Gamsol to thin oil paint,
linseed oil and oil paint mediums which include petrolium distilates (like Liquin) Stay away from household turps!)
1. You can't paint with acrylic on an oil-primed canvas
Acrylics are basically plastic (polymers), so they are not breathable. As oils age, they release gases. If you paint with acrylics on top of oil, these gases will cause the acrylic paint layer to crack and flake off as the gases try to escape.
2. You can paint with oil on an acrylic ('universally') primed canvas
3. If you use an oil-based primer, you need to size (seal) the canvas first
4. If you use a high quality acrylic primer, no sizing is needed
Let's first look at a few terms:
"Support" / "Substrate" - surface you are working on (i.e. raw canvas)
"Ground" = layer onto which paint is applied - the part you experience with your brush
"Size" = Sealant
"Primer" = "Ground" = provides tooth
"Gesso" = traditional (old) term for primer
"PVA" = Polyvinyl Acetate (size / primer)
"Acrylic Dispersion Ground" = acrylic gesso / acrylic primer (fulfills roles of size, primer and ground all in one)
""Tooth" = texture of a primed canvas (coarse, medium or fine)
Raw canvas needs a waterproof layer between itself and oil paint so as to prevent it from sinking into the cloth and causing discolouration and rotting.
Size is a sealant / glue that reduces the absorption ability of canvas and which prevents water / oil coming into contact with the fibers of the cloth, which will over time, irrevocably damage it.
Size also stiffens the canvas and reduces the amount of paint you use (or that is absorbed by the cloth)
Traditionally, rabbit skin glue was used to size canvas, but this is actually hygroscopic, and continuously absorbs moisture from the atmosphere, resulting in swelling and shrinking and eventual cracking of oil paint (which is brittle once dry)
The quality of your ground directly affects your painting experience and handling, how smoothly it glides over the surface and how quickly your paint dries.
Your primer is what creates this surface.
GESSO (pronounced 'jesso')
Traditionally, gesso is a primer - used to create texture on a canvas, but not all primers are gessos, since modern acrylic primers also contain a proper sizing agent, which gesso doesn't.
'Genuine ('traditional or 'glue') Gesso' is the term used to refer to a mixture of hot animal glue and gypsum or chalk (and sometimes pigment.)
It is hard and chalky and comprises of many thin layers that is sensitive to water and will crack if used on a flexible surface like canvas! To prevent cracking and delamination (due to Zinc Oxide contained in many genuine gessos) therefore, only use gesso on rigid substrates. Being very absorbent, traditional gesso (it will be labelled as such) is suited for painting egg tempura or encaustic. Otherwise labelled "gessos" are made with an acrylic ground and are actually not absorbent enough for this type of painting.
Stay away from PVA's that are not specifically formulated for artists!
Look for Ph-neutral or acid free. Anything else will lead to deterioration and must be avoided!
It generally has high acidity, does not retain flexibility and has high colour change and doesn't tighten the canvas like high quality acrylic primers do.
Priming is what gives your canvas texture / tooth, simultaneously stiffening and sealing the canvas.
Primer sticks better to your canvas than your medium would, essential to prevent your paint from flaking off once dry or delaminating when there is a sudden temperature change / the painting is removed from its stretcher or if it gets dropped / bumped, for example.
* PS - you don't need to prime unless you want the painting surface that priming gives - but then you have to size! You can paint directly onto modern size (not rabbit-skin glue!)
ACRYLIC DISPERSION GROUND
This is known as a "universal" / acrylic primer - fulfilling everything you need in one product.
It is water-based, and contains calcium carbonate (chalk), flexible acrylic polymer mediums (binder) / pigment (usually titanium white) and other chemicals to ensure flexibility, to ensure a long archival life.
It is not necessary to size a canvas before applying, since the acrylic polymers contained within the primer does this for you whilst providing the paint with something to properly stick to and provides a ground to paint on.
High quality acrylic primers are absorbent enough for your medium to physically merge with it, extending the longevity of your painting.
OIL / ALKALYD GROUNDS / PRIMERS
Oil primer is oil paint mixed with chalk to provide absorbency and tooth.
* You CANNOT paint with acrylic on an oil-primed ground
* Oil grounds can ONLY be applied over a size (otherwise the oil will be absorbed into the fibers of the cloth)
* Oil-primed canvases may appear yellow because of the linseed oil content
* Avoid lead oil-primers - these are dangerous and banned in some countries!
It is strongly recommended that you use oil / alkyd grounds on as rigid a support possible, to prevent cracking.
HOW DO WE PRIME OUR CANVAS AT ETH
Colour is the refraction of light. Light bouncing off a flat ('toothless') surface is quite, simply 'flatter'. Based on the science of the gold ball, tooth on a canvas not only grips your paint, but increases the surface area off of which light bounces, thereby making your colours 'pop'.
To achieve tooth, you need a priming process, which includes the application of a number of layers of primer, sanded with a fine water-grit paper between layers, and re-pulled to optimal tautness before receiving medium. And boy, does ETH achieve it!
Our signature, water-based acrylic dispersion ground was especially formulated with the longevity of both acrylic and oil paintings in mind, providing the perfect texture / tooth whilst remaining beautifully smooth for detailed work.
It adheres beautifully to the canvas, and provides a surface to which both mediums can stick, whilst simultaneously protecting the cloth from water and oil. It has plenty pigment and higher opacity than average primers that are commercially available.
Our canvasses are expertly primed (and sized) resulting in a texture that is perfect for any medium. In addition, our particular choice (weight and weave) of cotton duck contributes to the efficacy of this process: Tighter threads, woven in a stronger pattern. It’s quite simply a winning combination!
In summary - knowing the 'science' behind how your canvas responds to certain treatments will stand you in excellent stead to get the most out of your canvas, and a work that will last much longer than it otherwise would.
We offer white, clear and colour primed canvas.
If you are serious about your art, you need to choose the highest quality.
Your sanity (and reputation!) depends on it.