In order to get a surface upon which he could paint, he covered the panel with a thin coating of plaster which it was difficult to lay on absolutely flat.

Upon the plaster he drew the outline of the figures he was going to paint, and filled in the background with a thin layer of gold leaf, such as is to-day used for gilding frames.

After the background had been put in, it was impossible to correct the outline of the figures, and the labour of preparing the wooden panel and of laying the gold was so great that an artist would naturally not make risky attempts towards something new, lest he should spoil his work.

In the Jerusalem Chamber of Westminster Abbey there is a thirteenth-century altar-piece of this kind, and you can see the strips of vellum that were used to cover the joins of the different pieces of wood forming the panel, beneath the layer of plaster, which has now to a great extent peeled off.
The people liked to see their Old Testament stories and the stories from the Life of Christ painted over and over again.

They had become fond of the versions of the tales which they had known and seen painted when they were young, and did not wish them changed, so that the range of subjects was not large.