I talked to an expert that does this for a living. He said the  
following, neither CD or DVD is archive quality.

When DVDs were designed the requirement was that the glue that holds  
the layers together had to last three years. And under normal  
circumstances it will last at least that long. However, high heat or  
humidity can seriously effect longeavity. High heat is especially  
bad. In one instance my expert knows of a case where a DVD left in a  
mailbox in the SW in the summer completely de-laminated in a matter  
of hours.

Ordinary CDs are are probably a worse bet. At this point there is  
very little, if any, quality control (but given the price what do we  
expect) and a new CD may already have pits/bubbles/holes in the  
protective coating which will allow moisture to reach the data  
storage part. The thin coating on the back of CDs is the weak point.  
Anything that penetrates (and it can be scratched with a finger nail)  
that thin layer will allow moisture in and then it is only a matter  
of time before the data is lost. Gold CDs are better, but still not  
really a good place for an archive.

What companies who really care (advertising agencies, banks, etc.)  
use is hard drives that they completely recopy every three years.  
What you might want to do is buy a hard drive for archiving and also  
backup to DVD. Then store the DVDs in a low humidity and constant  
temperature environment. And of course every three years, or whenever  
there is a major software change do it all over again. My source also  
said to make sure that you use an open platform encoding DVD, not one  
specifically designed for graphics. That will better ensure that when  
it comes time to retrieve the image you can still read it. also do  
not use proprietary encoding. Use a commonly available image form.

There is one format that is archive quality, magneto optical (MO),  
they are good for 20-50 years. The only problem is that no one in the  
US, except for some specialty firms use them. We all dumped them for  
DVD/CD.

My source also said at this point just about nothing beats a good  
quality archival hard copy. So much for technology.

On Apr 23, 2006, at 17:37, Iain Stuart wrote:

> I am in the process of establishing my own consulting practice and  
> am thinking about how to store the digital images I am collecting.  
> The way to go seems to be to download them onto CD/DVD's. However  
> there is a problem with the longevity of CD/DVD's I think due to  
> the variable size of the 'silver or gold' covering the disc. I have  
> found lots of sites be archivists bemoaning this fact but with no  
> recommendations as to how to overcome the problem.
>
> Does anyone have any concrete advice or can point me to some  
> specifications I could look for on CD/DVD's?
>
> yours
>
> Dr Iain Stuart
> Partner
> JCIS Consultants
> P.O. Box 2397
> Burwood North, NSW 2134
> Ph/Fax 9701 0191
> [log in to unmask]