I usually remember quite a bit from books I've read even years later. Sometimes I may forget the title and start reading a book only to realize I have read it before once I get to a more distinctive section. Then I will only read it again if it really has something going for it. Classic works, on the other hand, I do remember reading and reread deliberately.
It gave me a strange feeling, though, when I realized that the book I read in under 4 hours was one I had read back in my teen years. I remembered absolutely nothing about the plot or even the characters. But I did remember the pearl necklace. In Anna and Her Daughters ( in which the good are rewarded as Wilde's Miss Prism asserts is the meaning of fiction) the narrator/heroine is given a very valuable pearl necklace to wear from the woman she works for. The woman explains that she had the wrong kind of skin for it, which caused the pearls to get discolored. Locking them up did not improve their conditions either. The young heroine agrees to wear them, and the pearls return to their original luster. The woman then tells her to keep them.
I read this 1958 book many decades after it was published, though quite a few years before Google, so I never looked into the question of curing sick pearls, as they are described in this book. Even with Google, I haven't been able to find much about it beyond an eHow piece that says dry conditions can cause pearls to turn yellow and that agrees with what the novel claims that pearls need to be worn to retain their luster. There is a comment on that article that gets rather scientific in describing what causes the discoloration and insisting that it can't be reversed:
There is no scientific evidence to back up the claim that wearing pearls will prevent them from turning yellow. Pearls turn yellow because they are made of an unstable substance called aragonite which due to the immutable laws of chemical science will eventually crystalize into calcite which is a more stable structure of calcium carbonate. Both substances are forms of calcium carbonate. Once this has happened the pearls turn yellow and nothing can reverse it. Oils in your skin cannot keep this from occurring, and there is no scientific evidence or even scientific conjecture to back up this idea. ''Drying out''from air tight storage might cause the nacre to peel but drying out does not hasten the process from aragonite to calcite which causes pearls to yellow. That process is hastened by moisture and heat.
The eHow articles that give tips on cleaning pearls also warn not to soak them because they will absorb the moisture and become soft. Sevenson's heroine, though, makes a special trip to the seaside to place the pearls in saltwater, as she has been told that will improve them. And the book that, in combination with her daily wearing, reverses the discoloration altogether.
On this reading, I realized that the author intends the pearls to function as a kind of symbol without having to make it explicit. It still strikes me, though, that the image of the sick pearls being cured by being worn as they should really stuck in my head for a couple of decades when nothing else in the book did.
Though I do tend to remember whodunit in mysteries, for other novels, concretely rendered images in books are much more memorable than plots.