A book rep first alerted me to the correct way of storing my artwork at the launch in Heffers of The Land of the Dragon King when my watercolours for that book were being returned to me after publication. He told me to protect them with an acid-free paper.
Last week I took a piece of artwork to a paper restorer after it came back from my American publisher creased. I learned from the paper restorer that the strippable board I used for my early illustrations, done in acrylic, was was not safe in the long-term. He told me to store my artwork without the CS board backing it - better still, mount it on an acid free board that would not affect it over the years.
As I'm in the process of selling artwork I feel I have a responsibility to sell something that is not going to deteriorate over the years. Thankfully, I've never used Doc Martin's inks that are popular with illustrators because of their vibrant colours but are known to fade badly with time.
I do sometimes wonder how much illustration there will be available for sale in the future when increasingly illustrators are using materials that don't last or are going in for computer generated art rather than illustrating in the traditional way.