What can I use to colour food grade Kaolin clay?

Question

I wish to use a food grade powder to colour clay powder, probably green or brown. I need a powder as the clay must remain dry. Clay is to be mixed in a ball mill along with Calcium and Potassium based products to make fertiliser pellets. (Not to make Ecstasy tablets or simmilar, saves you asking)

Answer 1

I do not think it is necessary to use an expensive food grade colourant for this application. My advice would be to go to your local hardware shop and I am sure that they sell colourants for mixing into building cement for making coloured plasters and groutings. This should be totally suitable for your use as a fertiliser colourant. The brown colour will probably be an iron oxide type . After all the fertiliser is going to be dug into the ground. Colourants containing lead etc, which had the potential to be toxic are no longer sold.

Later edit: I have now checked with my old employer before I retired. That is BASF. I am sure that there is a BASF office in a city near to where you are based - or check the BASF web. This company is probably the world's biggest producer of fertilizers and pigments. Chech with them and they will help, possible from their Heliogen or Pigmosol pigments range. They also have a range of Basovit colourants for food. But bearing in mind that the colourant is to be added(in a minute quantity) to kaolin and fertilizer plus some binding agent, none of which has food grade status I question why you need to use such a special colourant?