EN
The article contains a brief description of the history of canvas underpaintings, history of their manufacture and a description of the method for an analysis of the structure of old canvases. The method has been worked out in such a way as to ensure simple and easy studies in the conditions of each conservation workshop. The results obtained are useful as objective data, making it possible to documentate the structure of the canvas. Still, their main value consists in that they allow the conservator to investigate causative and effective connections taking place between the structure of the canvas and its functioning as painters' groundwork. The author discusses also problems of the behaviour of canvas underpaintings in a contact with water introduced during various conservation treatment or during an accidental flood. The structure of the canvas, its condition and finally the condition of the entire painting decide of the fact whether or not the contact with water will be harmful or relatively safe for the painting. The knowledge of dependencies governing the behaviour of canvases may enable the conservator to forsee the behaviour of paintings after the introduction of water. This kind of forseeing is of particular importance to works with 19th and 20th cent, paintings. The use of water agents is purposeful and advantageous in many cases but only after making sure that these are not canvases which will react with rapid shrinking that is harmful for a painter’s layer.