A stain is a discoloration that can be clearly distinguished from the surface, material, or medium it is found upon. They are caused by the chemical or physical interaction of two dissimilar materials. Accidental staining may make materials appear used, degraded or permanently unclean. Intentional staining is used in biochemical research and for artistic effect, such as wood staining, rust staining and stained glass.
There can be intentional stains (such as wood stains or paint), indicative stains (such as food coloring or adding a substance to make bacteria visible under a microscope), natural stains (such as rust on iron or a patina on bronze), and accidental stains such as ketchup and synthetic oil on a shirt.
Different types of material can be stained by different substances, and stain resistance is an important characteristic in modern textile engineering.
The primary method of stain formation is surface stains, where the staining substance is spilled out onto the surface or material and is trapped in the fibers, pores, indentations, or other capillary structures on the surface. The material that is trapped coats the underlying material, and the stain reflects back light according to its own color. Applying paint, spilled food, and wood stains are of this nature.
A secondary method of stain involves a chemical or molecular reaction between the material and the staining material. Many types of natural stains fall into this category.
In many cases, stains are affected by heat and may become reactive enough to bond with the underlying material. Applied heat, such as from ironing, dry cleaning or sunlight, can cause a chemical reaction on an otherwise removable stain, turning it into a chemical.
Various laundry techniques exist to attempt to remove or reduce existing stains. Stain remover is an important type of chemical in laundry detergents and some removers are formulated to be applied directly onto stains. The removal of some stains require other chemicals or special techniques. Use of an inappropriate technique could make permanent an otherwise removable stain or cause unwanted discolouration of the clothing.
- Stain removal guide, American Cleaning Institute
- Stain solutions, University of Illinois
- Stain removal advice from Procter & Gamble: UK, Canada
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- Solutions for Clothing and Laundry Stain Removal
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- Zia, Stephanie. Stain Removal. London: Hamlyn, 2005. Distributed in the U.S. and Canada by Sterling Pub. Co., 2005. 9780600611240
- Soto, Anne MarieStain Rescue!: The A-Z Guide to Removing Smudges, Spots & Other Spills By good Housekeeping Institute (New York, N.Y.). Published by Sterling Publishing Company, 2007 ISBN
- Mendelson, Cheryl Laundry: The Home Comforts Book of Caring for Clothes and Linens Simon & Schuster, 2005 ISBN 978-0-7432-7145-5