Chintz comes under the same unbrella as 'mercerized cottons' this means that the fabric surface is treated with caustic alkali under tention during the manufacturing to give it greater strength and this finish is what gives the surface of the fabric it's lustre or sheen. This made it very durable and hard wearing and was popular for soft furnishings, curtains cushions chair coverings etc.
(J Mercer (d 1866) patentee)
My Dad was a textile dyer, I learn't a lot about fabrics from him.
Gal