Put a cotton ball with clove oil in a palette that can be covered.  The clove oil will retard the drying of the paint. Clove oil contains eugenol which is an antioxidant.

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If clove oil retards drying it is NOT due to the mechanism having an antioxidant in it because the function of antioxidants work on a cellular level in living organisms and the last time I checked, oil paint is not a living organism.  If antioxidants were the key to retarding the drying of paint, an artist could put a slice of an orange or grapefruit and achieve the same oxygen-suppressing effect on paint, but I have serious doubts that this practice would work and would only result in a moldy piece of fruit in the middle of an artist’s palette.  If clove oil does retard drying, it is not the fact that it is an antioxidant.  The supposition of calling an antioxidant a substance that thwarts the oxidation of paint is based on a total misunderstanding of how biological chemical reactions work.  

While the addition of a cotton ball containing clove oil should not harm the paint and its ability to form a durable film, mixing clove oil into the paint will cause it to be compromised.  It retards the drying of oil paint and in turn inhibits the proper cross-linking of the oil molecules that display themselves as a hard, solid surface when dry.