Q: How I can reshape bristles that have been altered due to poor storage?
A: Brushes, especially high-quality ones, can actually be
quite resilient. Your problem can be solved easily with some gelatin or
mucilage, an aqueous solution similar to plant gum. Use a small amount
of this gelatin to moisten the brush hairs and then, while the hairs
are damp, press or mold them into the desired shape (think of the
gelatin as an adhesive that will hold the hairs in place). Leave the
brush to dry in this state. After a few days, wash out the gelatin, and
the brush should be back to its original shape.