Tutorial by Bet Borgeson
All art media, including oil and watercolor, have colors that fade or change with exposure to ultraviolet and visible light. This easy five-step test procedure can provide a better understanding of which of your own colors are resistant to light, without needing expensive test equipment or kits. It also discloses which pencils are fast faders, as well as those that fade very slowly.
STEP 1. On your drawing paper apply uniform rows of color at full strength, using maximum pencil pressure. Sample sizes might be about 2" high by 1/2" wide, with 1/4" spaces between them. Whether testing just one brand or more than one, try to group colors by hue family (all the reds, all the oranges, etc.). Identify each sample with its name and/or number.
STEP 2. Cut strips of foil about 3/8" wide and long enough to extend across an entire row of samples. Affix foil strips to samples as shown below, using snippets of masking tape here and there for a snug hold. Make intermittent pencil marks along edges of the foil strips.
STEP 3. Tape test sheet(s) to window, colors facing out. The window screen should be removed during testing.
STEP 4. After 10 full days of light (overcast days count as half-days) take the sheet(s) down. Row by row remove the foil, wipe away wax bloom if any, and glance at samples. Fading reveals itself in the uncovered areas as compared to the protected areas (which will remain unaffected by sun exposure). Just a quick glance is all that is needed to ascertain fading. Keep a list and note any faders you find. These are the fastest faders and should not be used in work to be sold or expected to last for years. Reposition your foil strips using the intermittent pencil marks as guides. Retape to window.
STEP 5. Repeat this process every 10 full days until tests have been exposed for 50 days altogether.
Results will vary slightly due to variations in geographical location and climate. But this procedure will give you a very good idea which pencils are the most light fast.
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