a pre-set time, usually 48 hours, when exposed to air. The replacement of the adhesive results in only minimal altering to the DVD manufacturing process. The time of the darkening can be influenced by varying the exact composition of the resin. For the DVD-5 discs, where there is no layer of bonding resin in the optical path, a surface coating can be used. According to the vendor, "Flexplay discs are fully recyclable and conform to all applicable EPA environmental standards." Some environmental groups have endorsed the product due to Flexplay's recycling plans and partnership with environmental industry leaders such as GreenDisk, leading to the creation of the first DVD recycling operation. Others such as the Grass Roots Recycling Network nevertheless have objected to the creation of a short-lived "disposable" version of a traditionally durable product. Chemistry The reactive layer contains a polymer resin that acts as a carrier for a suitable leuco dye, which, upon contact with atmospheric oxygen, oxidizes to form an opaque or semi-opaque material. Some of the dyes used are methylene blue, prussian blue, brilliant cresyl blue, Toluidine Blue O, Basic Blue 3, Methylene Green, Taylor's Blue, Janus Green B, Meldola's Blue, Thionin, Nile Blue, and Celestine Blue. The leuco dye is prepared by chemical reduction using a suitable reducing agent. The method commercially used by Flexplay and SpectraDisc employs methylene blue reduced by sodium dithionite. In order to prevent the oxidation from being triggered during manufacture of the discs, and in order to avoid the need for manufacturing in an inert atmosphere, the leuco dyes are further chemically modified to their blocked forms. Such blocked leuco dyes are the leuco dye precursors that form the leuco dye by a slow, controlled chemical reaction. Leucomethylene blue can be reacted with triisopropylsilyl trifluoromethanesulfonate, forming triisopropylsilyloxycarbonylleucomethylene blue (TIPSOCLMB), which is stable in presence of air oxygen. In presence of nucleophile reagents, e.g. water, the blocked leuco dye compound undergoes hydrolysis, releasing the unblocked leuco dye. This reaction is slow (several days to a week), and the hydrolytic compound is supplied either as atmospheric moisture, or in the formulation of the resin. The rate of the deblocked leuco dye oxidation is dependent on the pH of the resin polymer matrix. By adding basic compounds (for example, 1,4-diazabicyclo[2.2.2] octane (DABCO), or other amines), the pH is increased, and the reaction rate increases correspondingly. Correspondingly, by adding strong protic acids (for example,