Why must raw canvas be primed with gesso before applying oil paint?
ATo give the canvas a white surface so that paint colors appear more vivid
BTo seal the fabric and prevent the oil binder from soaking through, which causes paint to crack and canvas fibers to degrade
CTo increase the canvas's absorbency so paint soaks in more evenly
DTo make the canvas more rigid and prevent flexing during the painting process
The primary function of gesso is protective and structural: raw canvas is porous and slightly acidic. Oil paint applied directly causes the oil binder to seep into the fibers, leaving the pigment sitting dry on the surface where it will crack and flake; the canvas fibers also degrade from prolonged oil contact. Gesso seals the fabric (blocking oil penetration), creates tooth for adhesion, and establishes a neutral ground. Option A is true but secondary. Option C reverses the effect — gesso reduces absorbency by sealing, not increases it.
Question 2 True / False
For a very smooth surface suitable for detailed portraiture, the best approach is to apply more coats of gesso and sand more aggressively between each coat.
TTrue
FFalse
Answer: True
Surface smoothness is controlled by the number of gesso layers and the aggressiveness of sanding (220–320 grit sandpaper). More coats, each dried fully and sanded, progressively fill in the canvas texture. The result is a surface smooth enough for fine detail while retaining enough micro-texture for paint adhesion. Heavy impasto gesso (coarse brush or palette knife) produces the opposite — visible texture ridges that affect how paint sits. The choice of surface texture is an artistic decision made during preparation.
Question 3 True / False
One thick coat of gesso is preferable to multiple thin coats because it provides more material for paint to grip and saves preparation time.
TTrue
FFalse
Answer: False
Multiple thin coats produce a superior surface. A single thick coat tends to crack as it dries unevenly, creates inconsistent texture, and adheres less reliably. Thin coats dry more uniformly, bond better to each other, and allow precise texture control through sanding between layers. Two to three thin coats, each dried completely and lightly sanded, is the standard professional approach. The time investment in multiple layers pays off in surface quality that affects every subsequent paint layer.
Question 4 Short Answer
What does 'tooth' mean in the context of a primed canvas, and why does it matter for painting?
Think about your answer, then reveal below.
Model answer: 'Tooth' refers to the microscopic surface texture of the primed canvas — slight irregularities and ridges that give paint something to grip mechanically. When paint is applied to a surface with tooth, it fills these micro-valleys and locks in both mechanically and chemically. Without sufficient tooth (on an overly smooth or slick surface), paint slides around, refuses to adhere evenly, or peels over time. The amount of tooth is controlled by the number of gesso coats and how aggressively the surface is sanded: more sanding produces less tooth (smoother), less sanding retains more texture.
Understanding tooth connects the preparation step to its practical painting consequence. Students who skip priming or over-sand often encounter paint behavior they can't explain — too slippery, too streaky, lifting off instead of staying — without realizing that surface preparation was the variable. The tradeoff between smooth surface and tooth is an artistic and technical decision made before the first brushstroke.
Question 5 Multiple Choice
You want to begin a painting but find that every color you place on the white canvas looks darker than expected, making it hard to judge values accurately. What preparation technique would address this from the start?
AApply more coats of gesso to achieve a brighter white surface
BTone the ground by mixing a mid-value color into the final gesso layer or applying a thin wash over dried gesso
CUse only transparent glazes initially to avoid the value distortion
DWork on raw (unprimed) canvas, which has a more neutral natural color
Toning the ground eliminates the glare of pure white canvas, which causes every color placed on it to look darker than it will in context — systematically distorting value judgments from the first stroke. A mid-value toned ground (warm ochre, cool gray, muted earth) provides a middle reference: lights read lighter than the ground, darks read darker. This makes value assessment accurate from the beginning. Many painters consider untoned white canvas a hindrance rather than a starting point. Raw canvas (option D) also lacks the protection and tooth that gesso provides.