Hair Coloring 132 optimal to swell the hair to ensure good dye penetration and form the perhydroxyl anion required for lightening. For most shades the two bottles are mixed at a ratio of one part developer to one part tint. The development time for the final shade is typically between 20 and 40 minutes, depending on the level of gray coverage and lightening required. In the salon there are also two products, the tint and the developer, although the developer is often stored in larger bottles (~1 L) and then measured into a bowl with the tint and the two components are mixed before use. Table 4 Key List of Oxidative Dyes Primary Intermediates Couplers p-phenylene diamine Resorcinol 1,4-diamino-2-methylbenzyl sulfate 2-methylresorcinol 2-chloro-p-phenylenediamine 3-aminophenol p-aminophenol 2-methyl-5-aminophenol 2-amino-5-methylphenol 2-methyl-5-(hydroxyethylamino)phenol 4-amino-3-methylphenol 4-chlororesorcinol 1,4-diamino-2-(2-hydroxyethyl)-benzyl- sulfate 1,3-diamino-4-(2-hydroxyethoxy)- benzyl dihydrochloride 1-hydroxyethyl-4,5-diamino pyrazole sulfate 1-naphthol N,N-bis(2-hydroxyethyl)-p- phenylenediamine sulphate 5-amino-2-methyl-phenol 3-amino-6-methoxy-2-(methylamino)- pyridine dihydrochloride Application protocols vary widely, but in the salon the stylist will typically first apply the mixed product to the newly grown roots for a period of time before applying it to the bulk of the hair to match the color evenly from root to tip. Consumers applying themselves are generally less skilled, but some will apply product to the roots first before finally combing through, while others will just apply the product directly to the whole head at the same time. The salon will also sometimes use heat from a hair dryer during the application process, mostly to promote lightening for the lighter shades, or may cover the head with a plastic hood to conserve scalp heat.