There are several ways in which the special black cat bone can be procured. Here is a version from the Book of Saint Cyprian, the patron saint of the occult:
"Cook the body of a black cat in boiling water with white seeds and wood from the willow until the meat is loosened from the bones. Strain the bones in a linen cloth and, in front of the mirror, place the bones, one by one in your mouth, until you find that you have the magic to make you become invisible. Keep the bone with the magic property and, if you want to go somewhere without being seen, place the bone in your mouth."
Please note that I posted this to have merely informative value and I hope that none of You would even think of doing something this cruel and horrible as this This is and part of an article about black cats and magickal believes attuned with them and it is available at
http://www.mysticvoodoo.com/black-cat-folklore.htm
The painting is called The Love potion and depicts a witch with a black cat fammiliar by her feet
1903 painting by Evelyn de Morgan
I noted a curious lil thing , there is a couple outside the window , hmmmm maybe the witch is up to get that youngman