Epson Perfection V500 - Manual (Page 200)

a. transparency unit window
Make sure that no dust builds up on the surface of the document table or the transparency
unit window. Dust can cause spots in your scanned images.
Caution:
Do not press the glass surface of the document table with any force.
Be careful not to scratch or damage the glass surface of the document
table, and do not use a hard or abrasive brush to clean it. A damaged
glass surface can decrease the scan quality.
Never use alcohol, paint thinner, or corrosive solvent to clean the
scanner. These chemicals can damage the scanner components and the
case.
Be careful not to spill liquid into the scanner mechanism or electronic
components. This could permanently damage the mechanism and
circuitry.
Do not spray lubricants inside the scanner.
Never open the scanner case.