"Acid Free" is a term widely used in scrapbooking to describe paper that has not had acid used in its manufacture.
Paper can contain lignin, a chemical compound derived from the plant matter that gives it its strength. In time, lignin can cause deterioration of the paper, causing it to become yellow and brittle. It can also cause photographs to deteriorate.
But the biggest causes of deterioration of photos are moisture (increasing humidity), increasing temperature, air pollution and lignin.
Even grease from fingers can cause deterioration.
Many manufacturers also call this "archival safe".
Nowadays, most paper that is commercially produced is now safe. This is due to different manufacturing processes and techniques.
The best thing to do is to purchase safe products at a scrapbook supplies store or at a archival product store or website.
However, purchasing from these stores and websites does not necessarily mean that each product will be safe. We must learn to read the labels and the codes that mean that the product is safe.
If you're not clear about the products you're considering, then it's the best to ask the sales assistant or research the products online.
Even if you purchase your cardstock, scrapbook and photo albums from a scrapbook store and you're sure they're alright for scrapbooking your family history, there are still other hidden things that can do just as much damage to your memories:-
If you aren't sure that the paper you have purchased is acid and lignin free, it would be wise to use a pH-testing pen. These pens contain a solution that changes color if the scrapbooking item contains acid. However, they can not be used on dark-colored paper.
The extra time and effort it takes to look for archival safe products for your scrapbook will be well worth it when you scrapbooks are preserved for years to come.