If you can't obtain a crystal, it is possible to use a regular convex magnifying glass lens. Polished carefully and laid on the black velvet, it will work almost as well as the ball. Whichever you use, ball or lens, keep it purely for your scrying. Let no one else use it or even handle it. Keep it wrapped in a cloth (its black velvet or a piece of black silk) and do not permit sunlight to strike it. It is traditional to "charge" the crystal by holding it up to be struck by the light of the full moon, once a month.
A black gazing mirror seems to work better for some people than a crystal. It is not difficult to make one for yourself. You need a piece of glass, free of flaws and imperfections. Make it opaque by coating one side three times with asphaltum. To make the asphaltum stick to the glass, first clean the glass well with turpentine, then lay on the asphalt with a camel-hair brush.
A much easier method is simply to spray the back side of the glass with a good black enamel paint (it may not seem very magickal, but don't forget, the mirror is merely the focal point for your concentration. The actual "images" are projected by your powers; they do not come from within the mirror, or crystal, itself). A concave glass is the ideal. It is sometimes possible to find a convex glass from an old clock-face, in an antique store, and simply reverse it so that it is concave.
Place the glass in a frame. The shape is not important: round; oval; rectangular; square. Carve, or paint, onto the frame the names of the Lord and the Lady, in runes or one of the other magickal alphabets (see Lesson Twelve). As you are doing this—indeed, throughout the whole operation of making the mirror— concentrate your thoughts on the purpose of the mirror ... the projection of scenes from the past, present and future..
Consecrate the mirror in your circle, using the consecration ritual given in Lesson Five, naturally substituting the word "mirror" for "knife". When not in use, keep the mirror wrapped in a black cloth. To give you an easy start to scrying, before investing in a ball or making a mirror, try it with a glass of water. Just take a regular, clear water-glass and fill it with water. Gaze into that in the same way as described above. It should work quite well.