Most PC owners are aware that they should keep the glass surfaces of their monitor and scanner clean — but beware, because you can do more harm than good if you don’t know what you’re doing. Here are the guidelines that I recommend you follow when working with monitor and scanner glass:

• Abrasives are taboo! Even some household glass cleaners — which you might think could be trusted — can scratch the glass in your monitor or flatbed scanner when used with a rag or paper towel. With a scanner, small scratches can mean real trouble because a scratch can easily show up in your images at higher resolutions. Therefore, I recommend that you use only a dry, soft photographer’s lens cloth (which won’t scratch) or lens cloths with alcohol that are made specifically for monitors and scanners.

• Never spray liquids onto a flatbed scanner. If liquid gets under the glass and into the body of the scanner, you could end up with condensation on the inside of the scanner when you use it. Again, a dry, photographer’s lens cloth is a good choice . . . or pre-moistened lens cloths, which don’t carry enough alcohol to do any harm.

• Monitors should never be opened. Never take the cover off a cathode ray tube (CRT) monitor, even if it needs cleaning. Why? Well, your PC’s monitor is one of the two components of your system that carry enough voltage to seriously hurt you (the other being your PC’s power supply). If your monitor needs to be serviced or cleaned on the inside, take it to your local computer shop.

• Use a cover for your scanner. Scanners are somewhat different from most external peripherals. They don’t generate any heat while they’re on (unlike an external hard drive), and most of us only use a scanner once or twice a week. Therefore, your scanner is a perfect candidate for a cover that will keep it clean . . . and, by no small coincidence, you’ll find such covers at your local office supply store.