Wetting a canvas depends on your goal. There are several reasons you might want to wet a canvas, each with its own method.
Wetting a Canvas for Stretching
Some artists wet the back of a canvas after stretching to tighten it. However, this is controversial. Sources suggest this can lead to problems like tide lines (uneven drying causing streaks), loosening of the glue layers, and movement of grit within the canvas. Therefore, it's generally recommended to avoid wetting the canvas after stretching. Instead, ensure the canvas is properly stretched and dried before painting. [Source: The Picture Framers Grumble]
Wetting a Canvas for Painting (Wet-on-Wet Technique)
For acrylic painting techniques such as wet-on-wet, you might lightly wet the canvas with water before applying paint. However, acrylics generally don't support a fully saturated wet ground. [Source: Quora] Using too much water can lead to the paint pooling unevenly. If this happens, adding a flow release medium can help. [Source: Will Kemp Art School]
Wetting the Back of a Canvas Before Painting
As mentioned above, this is generally discouraged for stretched canvases. A YouTube video demonstrates spraying the back of the canvas (and the sides) thoroughly with water; however, it emphasizes that you need a way to dry it quickly. [Source: YouTube Video: "How to Tighten a Canvas with Water"] This method is likely more suitable for unstretched canvases or specific situations where the canvas is extremely loose.
Preparing a Canvas for Painting
Most commercially available canvases already have a layer of gesso, requiring minimal preparation beyond perhaps a thin layer of "liquid white" for certain painting styles. [Source: Reddit r/HappyTrees] Priming, the process of preparing the canvas with gesso or a similar medium, creates a suitable painting surface and prevents paint from sinking into the canvas. This process is typically done before wetting the canvas. [Source: Princeton Brush]
In summary: While there are situations where wetting a canvas might be necessary (such as tightening a stretched canvas—though discouraged—or using wet-on-wet techniques), it's crucial to understand the potential drawbacks and choose the appropriate method based on your goals. Generally, ensure the canvas is properly stretched and primed before wetting for painting.
