Here's my first attempt at a riddle,hopefully it's not too obvious. Please answer with explanations.
I have been on Earth too long to remember.
It can be said part of me is just ash.
But don't mistake me as immortal or black-hearted,
the more I work, the more white I become.
As a hobby,
I have composed lots of artworks you see in art museums,
just don't ask me to swim, I don't work well under water.
Who am I ?