# Supports, Stretchers, Sizing and Grounds

Painting I · Colour, Perception and Materials · https://tryals.app/learn/painting-i/supports-stretchers-sizing-and-grounds

## What the Paint Is Standing On

A painting is a layered stack. Each layer performs a distinct role:

* The **support** carries the entire structure.
* The **size** seals the support from oil.
* The **ground** provides a stable surface for the Paint.

### Supports

Panel provides a rigid surface, but it is heavy. Canvas is light and portable.

* **Linen**: Spun from flax with high tensile strength. It resists humidity changes.
* **Cotton duck**: Cheaper and weaker. It slackens in damp air and tightens in dry air.

Canvas frames come in two types:

* A **stretcher** has expandable keyed corners to adjust tension.
* A **strainer** has fixed corners and cannot be adjusted.

### Sizing and Grounds

Drying oils rot raw cellulose fibres. **Size** seals the fabric to prevent this decay.

* Animal glue size is prepared at **7 per cent by weight in water**, or 70 grams per litre.
* A modern **PVA size** is non-hygroscopic and will not crack canvas with humidity changes.

### Grounds

| Ground | Composition | Best used on |
|---|---|---|
| Traditional gesso | Chalk or gypsum in glue | Rigid panel only |
| Oil ground | White pigment in Drying oil | Canvas or panel |
| Acrylic primer | Pigment in acrylic emulsion | Canvas or panel |

> **Common pitfall:** omitting the size layer. Raw canvas will turn brittle and rot under oil paint.

## Practice questions

9 of this lesson's 14 practice questions, with answers. The full set is in the app.

### 1. A student stretches raw cotton duck and paints straight onto it in oil, with no size and no ground. Ten years later the paint film looks sound but the cloth behind it is brown and snaps when flexed. Why has the fabric failed while the paint has not?

A. Ambient moisture oxidised bare cotton as omitting a ground exposed it to humidity shifts
B. Heavy pigment particles penetrated unsealed weave over time, abrading fibres from within
C. Free fatty acids in drying oil rotted cellulose in direct contact, which size prevents
D. Contraction of the oil film during cross-linking caused tension that tore yarn fibres

**Answer:** C. Free fatty acids in drying oil rotted cellulose in direct contact, which size prevents

**Why:** The oil attacked the fibre. Its free fatty acids degrade cellulose on contact, embrittling the cloth while the film above stays healthy, and the oil soaks through and stains as it goes. A size layer isolates the two, which is why it is the least visible and least optional layer in the stack.

Page: https://tryals.app/practice/painting-i/supports-stretchers-sizing-and-grounds/a-student-stretches-raw-cotton-duck-and-paints-straight-onto-it-in

### 2. A traditional gesso of chalk and animal glue is too brittle for a flexible canvas and belongs on a rigid panel.

**Answer:** True

**Why:** **True**, and the naming is what causes the trouble. Real gesso is chalk or gypsum in animal glue, hard and inflexible, and it crazes on anything that flexes. The tub sold as acrylic gesso contains no gesso: it is a flexible dispersion that merely occupies the same place in the stack.

Page: https://tryals.app/practice/painting-i/supports-stretchers-sizing-and-grounds/a-traditional-gesso-of-chalk-and-animal-glue-is-too-brittle-for-a

### 3. Complete the account of the layers under the paint.

**Answer:** The traditional sealing layer between fabric and ground is rabbit-skin **glue**, commonly made at about seven per cent by weight in water. A frame whose corners can be driven apart to re-tension the cloth is a **stretcher**, while a fixed one is a strainer. The thin toned layer laid over the ground before painting is the **imprimatura**. Cotton duck is more **hygroscopic** than linen and therefore slackens and tightens with the weather.

**Why:** The second blank is a distinction worth keeping. Every canvas slackens eventually, and a strainer offers no way to answer that except restretching the whole picture, which is why a strainer is a decision about the next fifty years disguised as a saving of a few euros.

Page: https://tryals.app/practice/painting-i/supports-stretchers-sizing-and-grounds/complete-the-account-of-the-layers-under-the-paint

### 4. Which of these are true of linen compared with cotton duck?

A. Linen changes dimension less with humidity than cotton does
B. Weight classes such as "medium" are a supplier's classification rather than a standard
C. Linen has longer fibres and higher tensile strength
D. Linen is cheaper per square metre than cotton duck

**Answer:** A. Linen changes dimension less with humidity than cotton does; B. Weight classes such as "medium" are a supplier's classification rather than a standard; C. Linen has longer fibres and higher tensile strength

**Why:** The third is the practical one. Two rolls both labelled medium weight can differ substantially, so the only comparison worth making is the weight per square metre and the thread count printed on the roll, the words on the label carry no guarantee at all.

Page: https://tryals.app/practice/painting-i/supports-stretchers-sizing-and-grounds/which-of-these-are-true-of-linen-compared-with-cotton-duck

### 5. Strainers feature fixed joins whereas stretchers use keyed corners. Why does this structural difference matter more when preparing cotton duck than linen?

A. Cotton fibres lose tensile strength whenever sized with PVA
B. Linen rots faster when keyed corners let moisture enter
C. Strainers fail to distribute the high mass of raw linen
D. Cotton contracts in dry air and slackens in damp air

**Answer:** D. Cotton contracts in dry air and slackens in damp air

**Why:** Cotton duck responds actively to atmospheric humidity swings by sagging or over-tightening, demanding expandable corners to correct tension. Linen resists moisture movement far better, while neither PVA nor moisture ingress at corners alters these structural behaviours.

Page: https://tryals.app/practice/painting-i/supports-stretchers-sizing-and-grounds/strainers-feature-fixed-joins-whereas-stretchers-use-keyed-corners

### 6. Match each layer to the job it does.

**Answer:**

- Size → Isolates the fabric from the oil that would attack it
- Ground → Supplies a surface of known absorbency and colour
- Imprimatura → Kills the white and sets a mid tone to judge against
- Varnish → Adds a removable protective and optical layer at the end

**Why:** Only the last is designed to be removed, and that is a working definition of a varnish rather than an incidental property. Anything applied over a finished painting that cannot be taken off again is part of the painting, whatever the tin calls it.

Page: https://tryals.app/practice/painting-i/supports-stretchers-sizing-and-grounds/match-each-layer-to-the-job-it-does

### 7. Arrange the layers of a traditional oil painting in order from the support outwards.

**Answer:**

1. The support: panel or stretched cloth
2. The size that seals it
3. The ground that supplies the working surface
4. The imprimatura that kills the white
5. The paint layers
6. The varnish, applied once the film is dry through

**Why:** The sequence is also a timetable. Everything up to the paint happens in a week; the varnish waits for the film to be dry through, which for an ordinary oil painting is conventionally at least six months and depends on thickness, pigment and the room it dried in.

Page: https://tryals.app/practice/painting-i/supports-stretchers-sizing-and-grounds/arrange-the-layers-of-a-traditional-oil-painting-in-order-from-the

### 8. The tub sold as acrylic gesso is traditional gesso supplied ready-mixed, which saves making it up from chalk and glue.

**Answer:** False

**Why:** **False.** It contains no gesso: it is titanium white and chalk in an acrylic dispersion, flexible enough for canvas precisely because it is not the brittle chalk-and-glue material. The shared name is the reason students prime canvases with something that cracks.

Page: https://tryals.app/practice/painting-i/supports-stretchers-sizing-and-grounds/the-tub-sold-as-acrylic-gesso-is-traditional-gesso-supplied

### 9. A canvas 1.2 metres by 0.9 metres is to be sized. At a coverage of about 8 square metres per litre, how many millilitres does one coat need?

**Answer:** 135 (within ±15)

**Why:** About **135 ml**. The area is 1.08 square metres and 1.08 divided by 8 is 0.135 litres. The coverage figure is a property of the particular size and the absorbency of the cloth rather than a constant, so it is worth measuring once on your own materials and writing it down.

Page: https://tryals.app/practice/painting-i/supports-stretchers-sizing-and-grounds/a-canvas-1-2-metres-by-0-9-metres-is-to-be-sized-at-a-coverage-of