We have a job right now that started from linseed soaked rags. They were left overnight in a plastic bucket. They ignited, after smoldering for hours by spontaneous combustion.
PLEASE be careful with any cloth soaked with paint thinners and such. They can be very dangerous. These people were asleep when the smoke detectors went off in the middle of the night. Everyone got out safely, thank goodness.
Keep these things outside after using in a metal container.
Just good information to keep in mind.