Q. I have a big box of 35mm mostly Kodachrome slides taken over the past 50 years or more. I would like to scan them and burn them onto...

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Q. I have a big box of 35mm mostly Kodachrome slides taken over the past 50 years or more. I would like to scan them and burn them onto optical disks, then catalog them so that I can find what I want quickly and easily. So I am thinking the largest capacity DVD media would be a desirable choice. But I have not found anything on the archival longevity of DVD media.

— John Tate

A. I’ve seen estimates ranging from 10 years to 100 years for the life span of data stored on CDs and DVDs. Commercially produced discs, created by the etching of pits and grooves in the disc, just as with old-fashioned LPs, tend to have a longer life span that discs burned by consumers. The latter method of storing data relies on shining lasers on a dye in the disc material. That dye is prone to breaking down over time.

CDs and DVDs are also prone to some of the hazards of old-fashioned LPs, which are also made of plastic. Leave a CD or DVD lying in the sun for long, for example, and you’ll find your data can’t be read.

The lamination process may also affect the life span of discs. If the process is done too quickly during manufacturing and the adhesives are not allowed to cure fully, the discs may delaminate.

In short, steps some disc manufactures may take to save pennies could result in the disc breaking down sooner. While you don’t always want to pay top price for CD and DVD media the rule of thumb is generally: “You get what you pay for.” If you buy the cheapest discs, don’t be surprised if they break down sooner. Will you care if your DVD breaks down in 25 years? If not, use the less expensive ones.

There are some things you can do to keep your discs in good condition. Keep them stored in a cool place and avoid direct sunlight. Keep them in jewel cases. Handle them by their outer edges. If they get dirty, use deionized or distilled water to clean them, wiping them down with clean cotton fabric from the center of the disc to the outside, rather than wiping along the grooves. If water isn’t enough, use diluted rubbing alcohol or dish detergent, taking care to rinse the disc thoroughly.

By the way, photographic slides also have a great deal of variability in life span. I’d be very surprised if those 50-year-old slides haven’t shown significant changes. The variability depends on not only the original quality of their material and dyes, but also on the conditions in which they have been stored.

While storage of images on CDs and DVDs does offer some potential benefits in longevity over slides there are also some unique risks. Because the data are stored digitally, you’re counting on the format to be supported by software available 100 years from now. You might have a 100-year-old CD that’s in great shape but there’s no software to read it.

Q. When I open my laptop at our office, I find three or four strong signals from unsecured Wi-Fi sources, probably from apartments and houses right next door. I click on my browser and enjoy excellent Internet access. I know, bad security risk.

My question: Can a Wi-Fi router owner easily detect data transfers to and from something “out there”? I have a Netgear wireless router at home. I hadn’t found anything in the software that would alert me when data transfers are happening outside my own stuff.

— Stuart Stovin

A. What you’re looking for is called an “intrusion detection” device. They are generally not built into routers and they do require a fair bit of expertise to be useful. Most home or small-office wireless users would do best to focus on implementing available measures to secure the access point. Most especially, it’s important to turn off the access point’s broadcast of its station identifier and to require all traffic to be encrypted.

Yes, the encryption key can be relatively quickly hacked by someone who knows what they’re doing, but at least you’ll be protected from casual intruders.

Questions for Patrick Marshall may be sent by e-mail to pmarshall@seattletimes.com or pgmarshall@pgmarshall.net, or by mail at Q&A/Technology, The Seattle Times, P.O. Box 70, Seattle, WA 98111. More columns at www.seattletimes.com/columnists.