They are more expensive than other dyes because of the rigorous and costly toxicity testing required for food additives. Aniline dyes are available in brilliant colours although the suspected carcinogenic properties of some limits their use. Basic dyes are widely used and give good results. They have a low affinity for cellulose and hence are less likely to result in patchy dyeing. Of the textile dyes, the 'direct' class being designed for dyeing cotton, are quite likely to give good results for dip dyeing of whole plant material.
Direct dyes are cheap, easy to apply and widely available in a range of colours.
Table 1 lists trade names and suppliers for the different dye classes. Manufacturers rarely sell dyestuffs in small quantities than 25 kilograms. Some common biological stains are listed in Table 2 and some inorganic colouring compounds in Table 3 . These are available either from dye manufacturers or chemical supply houses. Table 1 .