Why Cracks Appear in Oil Paint
|Reasons for a Cracking Oil Painting|
Oil Painting Do’s and Don’ts
Investing a lot of time in an oil painting deserves the best art materials, or the time will be wasted. The following advice will help prevent the frustration of a cracking oil painting.
As with anything, never use a substitute product for the one that is designed for oil painting. For instance, avoid using household emulsions or cheap primers to prepare the painting support. Some of these may not provide a sufficient barrier against the absorbent properties of the canvas or board. The result of this is that the still-absorbent support will suck the oil vehicle from the paint, causing it to brittle, and cracking may result. Stick to a recommended oil painting primer, such as Winsor & Newton or Daler Rowney, although a good quality acrylic primer is fine for oil sketches or quick studies.
Do not use mediums and solvents designed for household or industrial use in place of those specifically designed for oil painting. They can affect the permanence of the pigments. Turps, paint strippers and household varnishes will also ruin art brushes and emit powerful odours. Stick to artist’s agents such as Sansador or artist oil painting varnishes.
Never combine mediums with varying drying rates, such as stand oil (which dries slowly) with alkyd mediums (which dry quickly) in the same painting. This will cause stresses in the painting layer as it dries and inevitable cracking. Stick to the same medium in any one painting.
What is the Fat Over Lean Rule?
When working in layers such as when glazing with oil colours, introduce a little more oil medium into your oil paints. This practice merely entails mixing a little oil with the pigment before applying it to the painting. Known as “fat over lean” or “flexible or inflexible,” this practice provides flexibility to the upper layers of paint and will prevent it from cracking.
Linseed oil is most commonly used for fat over lean, but other oils are suitable, such as stand oil, safflower oil or oil of spike lavender. However, it is best to stick to the same oil medium for each painting as this will prevent conflicting drying rates in the paint.
Proper Use Of Oil Painting Products
Always read the manufacturers’ instructions properly, as some art products might require special preparations. Items such as rabbit skin glue or oil primers often need to be used in a specific way.
Never varnish an oil painting until it is thoroughly dry. Oil paint that is not quite dry could adhere to the varnish layer and cause it to “move” with the varnish as it dries and contracts, causing the oil paint to crack. Further problems may present themselves in the future when it comes to removing the varnish for cleaning, as some of the oil paint may come off with it the varnish.
Art Materials to Prevent Cracking in Oil Paint
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Any oily art medium can be used for the fat over lean rule to prevent the upper glazes of oil paint from cracking but linseed oil is most often applied. Artist varnishes are available for any finish from matt to gloss, so long as the oil paint is thoroughly dry (after six months or so). With this in mind, oil paint is a very forgiving medium, and few artists have encountered cracking in their oil painting, even with short cuts.
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