How do I add Borax to milk paint?

Only need milk & acidic source(vinegar or lemon,or lime)along with some acrylic paint or dry color pigment. Here's milk paint recipe https://www.marthastewart.com/272306/milk-paint-recipe " If yours turns out lumpy, you can add borax or bicarbonate soda to smooth it out. Just be sure to use it the day you make it (and therefore only make it in the quantities you need) because, like milk, it will spoil! " here's more on it https://food52.com/blog/17483-a-paint-with-character-and-how-to-make-it-from-milk

Thanks. I didn’t realize that the lime/lemon (acid) juice used to mix with the milk was different than the lime paste that some recipes used. I have fresh squeezed lime juice prepared to add to the curd like stuff, instead of lime( base) paste. I’m just going to use the Borax and see how it goes. Wish me luck😀Thanks for responding so quickly.