Materials: A work of art will last as long as the materials. If longevity is a concern when you purchase art, then you should do a little research on materials. In my research on materials, I found that the most trusted names in manufacturers have sold suspect materials for decades just because artists demanded them, and in turn artists assumed they were buying good materials, because of the brand name.
My Materials: In my original watercolors, I use only Arches watercolor paper. It is 100% cotton and acid-free. I use only paints that contain pigments that have been rated "lightfast" by ASTM (The American Society of Testing and Materials). I have found that many people are under the impression that only oil paintings are "permanent". It is true that pigments that are not "lightfast" will last longer in oil than when applied as watercolor. It is also true that pigments that are lightfast on paper are permanent, just as permanent as they are in oil. We've all seen inexpensive prints or photographic images fade, yellow, or darken over time. It is important to know your materials. Inks and photographic chemicals are reactive to light (they fade or darken with exposure) Also, most paper is made from wood pulp and is quite acidic. It turns yellow very rapidly.
My original watercolor paintings are painted on non-yellowing, acid-free paper. They are painted with the same permanent pigments found in high-quality oil paintings. They will not fade, darken or yellow. Many people think art should only be hung in a poorly lit room. I suspect this is because art museums hang their paintings in dim galleries. The reason this is done is because museum paintings contain the many light-sensitive, "fugitive" pigments that were available to early artists. They have to be hung in dim light. I hang my paintings in my sunny living room and light-washed studio. I'm not worried about the materials, because I know what's in them.
Why buy an Original Work? When you purchase an original work of art, you become an Art Patron. You are actually "paying an artist's salary" to work for you. You are buying years of education, experience, experiments, successes and failures. And, the work you purchase is unique in the world.
My humble philosophy of art as it stands today; the one that works for me, anyway.
Art is process, not product. A painting is a vehicle of art. If you're lucky, it will allow someone to share what you felt when you painted it: wonder, joy, peacefulness, aloneness, a misty morning in the forest, etc. I think great art, whether it's painting, film, music, etc, makes us feel more connected to other people. Experiencing art makes us part of the process. It connects us over distance and cultures, and even into the past and future.