Photochromic compounds change colour on exposure to light, while the reversion may be attributable either to radiation or may be thermal. The use of photochromism on fabrics can provide new opportunities to develop smart textiles; for example, sensors and active protective clothes. Ethyl cellulose-1,3-dihydro-1,3,3,4,5 (and 1,3,3,5,6) -pentamethyl-spiro-[2H-indole-2,3′-(3H)naphtha(2,1-b)(1,4)oxazine] composites were prepared by an oil-in-water emulsion, solvent evaporation method in order to form easily suspendable and fatigue-resistant photochromic nanoparticles in screen-printing paste. Their size was well below 1 μm and did not change substantially over a wide range of dye concentrations. After screen-printing, a homogenous photochromic layer was built on a cotton substrate surface, which represented substantial blue colour development in CIELab colour space measurements because of ultraviolet light, even at a dye concentration of 0.045% w/w. The addition of a photodegradation inhibitor, Tinuvin 144, further increased the coloration of the printed fabric
