Each stamp gives you a way to "dress up" bar soap in both the melt and pour or cold-process.
To create an impression in soap, center the image end of the stamp on the soap then lightly tap the wooden end of the stamp with a hammer 2 to 3 times. A regular hammer works well, but wooden or rubber mallets are gentler on the wood. Practice on scrap soap to get comfortable with the process.
A flat soap surface allows for even, consistent images. You don't need to stamp too deep- about 1/8 inch is plenty. The deeper the impression, the more soap is displaced, which can warp the outer edges of the bar. Smaller bars can be stamped to a lesser depth to avoid warping or breakage.
Depending upon the formulation of your soap, the soap may be ready for stamping as soon as it's unmolded. Softer and/or super fatted soaps may require a few days of aging. The soap should not stick to the stamp; if it does, the soap needs to harden a bit.
Stamped designs show up best on colored bars. White soap reflects light, resulting in less contrast between shadow and light in the image. One way to create contrast in a white bar is to dip the stamp in dye, following the instructions given two paragraphs below.
Milky Way soap stamps work in cold-process as well as melt and pour soaps. Melt and pour soap base tends to be firmer and more brittle than cold-process soap, and the stamps may consequently require an extra tap or two to register a satisfactory image. If you wish to soften the M&P soap base, add 1-2 ounces water to each pound of base. The stamped images in this softer soap display a smoother, more polished finish. After stamping, age the bars a few days to allow for evaporation of excess water.
A simple, beautiful way to add even more visual contrast to the stamped image is through the use of dyes. Purchase un-inked stamp pads at any office supply store, then ink the pads using ordinary liquid food coloring or your favorite FD&C dye. Press the soap stamp into the pad enough to obtain a light, uniform coating of dye. Now tap the image into the soap. If you're using powdered dyes, try experimenting with different dye saturations for varying degrees of contrast.
After use, clean the stamps using a brush and water. Dry thoroughly before storing.
Saturate ink pad with food coloring or your favorite soap colorant, then ink the soap stamp. Tap the stamp into soap. The dye creates a lovely "background" and adds an extra dimension to the stamped image.