Photopia AQ Ink is an organic photochromic colourant that changes colour reversibly and repeatedly. The UV sensitive product line by Matsui is available in three reversible colours: yellow, purple and blue. Each colourant comes as a powdered form with a light colour.

The colours are activated when exposed to the sun or other ultraviolet light sources and then change from clear to colour. They change back to clear when the ultraviolet light source is removed.

The coating is available in an AQ and gravure ink formats, plastic resin concentrates, PVC spray and powders. The powder is insoluble in water but is soluble in most organic solvents.

For moulding purposes, the coating is heated and kneaded into a resin such as polypropylene or polyethylene. EVA and K-resin can also be used. Moulding the mixture of colourant and resin can be performed with injection moulding, blow moulding or extrusion machines.

For preparation, each colour has a different melting point. Yellow melts around 162 °C, purple around 237 °C and blue around 257 °C.

Using other white pigmen6ts together will also decrease concentration of colour exhibition through light and light fastness. For moulding with a high concentration of colour exhibition, the manufacturer recommends mixing the ink into a transparent plastic.

Applications are varied, though recommended for interior use. Examples include stationery, clothing, uv indicators, light adjusting film and sunglasses.