|MadSci Network: Chemistry|
Dear Katie, The difference between a permanent and a dry-erase marker is small. Actually, a dry-erase marker IS a permanent marker on any surface that is porous (like paper) as opposed to glass, metal, some plastics, and dry- erase boards (whiteboards). When comparing both types of ink, the dry- erase ink has the same basic ingredients as the permanent type: colored pigments, "carrier" (water, alcohol or another solvent) and polymer. The difference lies in which polymer is used: for permanent markers, acrylic polymers are often used...these polymers are also used in house paints to make the pigment stick to the walls. For dry-erase markers, an oily silicone polymer ("release agent") is added; the oily film it makes serves as a lubricating barrier that keeps the colored pigment from touching and staining the whiteboard. The silicone polymer is so slippery that it just slides off of the whiteboard, taking the pigment with it. So, in order to make a dry-erase marker ink permanent ON A WHITEBOARD, a polymer must be added to make the pigment stick, such as I described earlier that acts like a glue for nonporous surfaces like whiteboards.
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