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First scrape off as much as possible with a dull knife. Hot soapy water will then remove fresh stains from washable articles. If a brown stain remains, soak in a solution of a diaper wash/sanitiser container sodium percarbonate followed by a good rinse in warm water.
For unwashable materials, sponge with dry cleaning fluid. Allow to dry. Repeat as necessary with a clean portion of pad beneath. If any mark remains, sponge with equal quantities of methylated spirits (wood alcohol) and household ammonia (test on colours first). Follow with warm water. A spray-on dry cleaner may be used.