Practice question · Multiple choice
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?
Hints
- Ask what oil does chemically to cellulose it is touching.
- The layer that was left out has exactly one job.
Show the 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.
Practise Supports, Stretchers, Sizing and Grounds
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