B Bolthouse

John Seymour in his book self sufficiency  says
"Very good paints can be made from a mixture of sour milk, hydrated (slaked) lime, and any coloured earth pigment that you can find. The lime and the sour milk must have neutralized each other, and this can be tested with litmus paper: if the paper turns red add more lime, if it turns blue add more sour milk. The pigment that you add to this is any strongly coloured earth, sediment or clay. Dig it out and boil it in water several times, each time in new water. Strain off the water and dry- the sediment in a warm place. Pulverize it as finely as you can and store. Mix this powder with the milk-lime mixture until you get the colour you want. Keen paint-makers keep an eye out as they travel about the countryside for any colourful looking earth or clay, and grab it when they see it. "

if you want something a bit more holdfast than chalk

I found the part in the second edition of tree crops, "W H Mills, professor of rural sociology at clemson college, south carolina, called my attention to the privet. he said 'it is commonly used with us as a hedge plant, but after birds scattered the seeds it is found growing wild.  For some years i have been feeding my chivkens in increasing quantities, as i have found no ill effects fromits continued use.  The chickens began to eat the seed as soon as they ripen.  Such is the abundance of the crop that the seeds usually hang on the trees until the middlr of February or March when the cedar waxwing birds in the migration north stop long enough to clean the trees.  I believe that we can have at practically no cost a supply of poultry feed for two or three months duringthe winter from this source.  I am enclosing an analysis which i got from the chemist of the south carolina experimental station to make some two or three years ago.'"

I remember privet being mentioned in "Tree Crops - A Permanent Agriculture" as a good food source for chickens, but i cannot find the page now.  Seeing how productive and dense a privet hedge can be, it could work well.