Seed Dressings

Seed is coloured for tax purposes, identification of pesticides, and to mark grains for animal
feed or destruction.

a) Powder Seed Dressings
These are based on extenders such as talc or China clay which can be dry blended with
pigments. The preferred method of colouring is to use the pigment to prepare a masterbach
which is then blended with the remaining clay.

Occasionally basic dyes can be used to mark seeds for destruction.

b) Liquid Seed Dressings
These can be formulated in glycol ether or water/glycol ether and are coloured with
approximately 1% of a SULFACIDE acid dyestuff. Mainly red shades are used as other colours
tend to imply faulty seeds.

The dressing is applied to give aproximately 0.002% on seeds or less than 1ppm dye. Basic
dyes are used less frequently, but give good colour intensity.

Fertilisers

a) Solid Granules
Beads, granules or pellets can be coloured with pigments, preferably dry ground onto an
extender such as China clay. Basic dyes can also be used by spraying aqueous dye solution
onto China clay which is then dry mixed with the fertiliser.

The concentration of colour in the final fertiliser is of the order of 0.003% for pigment and
0.003% in the case of liquid basic dyes. This corresponds to first uniformly mixing 3 parts
pigment with 100 parts Kaolin, then adding this to 100 times the weight of the fertiliser beads.
Alternatively 3 parts of liquid basic dye are diluted in approximately 50 parts water and sprayed
onto 1000 parts Kaolin. This is again dry mixed with 100 times the weight of fertiliser beads.

b) Liquid fertilisers
These formulations are based on soluble electrolytes and are coloured with water soluble
SULFACIDE acid dyestuffs stable in the system.

Poisonous Baits

Slug bait is made more attractive to pests by colouring blue, usually with a pigment like
BRICOFOR Blue A4RP.

Rat poison is also coloured blue or red with pigments to draw attention to their toxic nature.

Herbicides, Pesticides, Fungicides

Weedkillers tend to be specific in their application and are normally coloured to prevent
misuse. Blue is usually selected and must be stable for long periods of storage even at tropical
temparatures. Suspension concentrates in water are usually coloured with SULFACIDE acid
dyes (0.05%) or pigments (0.01%).

Emulsifiable concentrates are solvents which can be coloured with solvent dyes (KENAWAX).
Products insoluble in water are sold as wettable powders based on China clay which disperses
in water for spraying. These are coloured using pigments.

Aerial Crop Spraying

Basic dyes are used to mark areas sprayed with agrochemicals to ensure that produce is not
overdosed by double spraying. The lowest possible concentration of dye is used consistent with
clear marking. The basic dyes have poor light fastness and chemical stability so that the colour
soon fades.

The fugitive marking of lawn dressings can be achieved by using an acid dyestuff of approved
hazard rating, eg SULFACIDE Brilliant Blue 5J50.

Hazard Legislation

Agricultural chemicals are the subject of legislation based on environmental pressures. There are
no clear guidelines applicable to all countries, though the presence of a colorant in US legislation
implies worldwide acceptance. Although the colour is a minor percantage of the toxic agrochemical
the toxiocants are degradable and therefore the colorant must become equally harmless less it
accumulates in the soil.

The use of colour additives in the USA is controlled by the Food and Drug Administration and
permitted colours are listed in the Federal Register. Colours given FD & C numbers are approved
for Food, Drugs and Cosmetics while those with D & C numbers are approved for Drugs and
Cosmetics only. The status of dyes is reviewed periodically and can be either permanent or
provisional.

The colours listed in the Colorants with Equivalent Food & Drug Administration Numbers table
below are the same active chemicals approved in the register, although full approval is subject to
limitations and restrictions on purity. This list does not guarantee approval in every country so
that formulators should not be restricted in choice as many other dyes are equally suitable.

Agrochemical Colorants