Pour 3/4 cup hydrated lime powder, available at hardware and home improvement stores, into a plastic bowl.
Add 1 1/2 cups water to the mixture and stir with a wooden paint stick until the ingredients are well incorporated. Set the bowl aside.
Pour 1 quart room-temperature skim milk into a separate bowl. Add the juice of one entire lemon or lime to the bowl and stir until the ingredients are well incorporated.
Allow the milk to remain on the kitchen counter overnight. This will curdle the milk, separating the casein from the non-essential elements of the liquid.
Cover a bowl with cheesecloth and pour the mixture through to separate the curds and whey. Discard the liquid portion of the bowl and pour the curds into a plastic bucket. Break up any larger curd chunks with your hands or a spoon.
Add the lime mixture to the plastic bucket. Stir the ingredients together until all of the curd chunks are completely dissolved and the mixture takes on a creamy consistency.
Add 1 tbsp. dried pigment powder, available at craft stores, to the plastic bucket. Stir the powder into the mixture. Continue to add powder to the mixture until you achieve the desired color.
Set the furniture onto a pile of newspaper. Pour the milk paint into a paint tray and apply it with a paint brush or roller, depending upon the size of the piece.
Allow the first coat of milk paint to dry before applying a second and third, if desired. Let the final paint coat dry completely before continuing. The amount of time it takes for the milk paint to dry depends upon the air temperature and humidity.
Apply a thin layer of boiled linseed oil to the furniture with a rag to seal the paint. Allow the linseed oil to set for 10 minutes before wiping any excess away with a clean rag.