Here are some recipes to get you started. They are simple pours in the various kinds of molds. You can, of course, use these soaps just as they are when they're hardened. Make a trip to the craft store and choose some basics: a base, a color, a glittery mica, and a scent. Get a few different kinds of molds. Keep in mind that food coloring isn't light-stable and will fade with exposure to light. For your first experiments, this shouldn't be a problem. If lightfastness is an issue for you right away, get some lightfast colorants that are made especially for soap.
Basic Block Mold
1 pound soap base, roughly chopped into 1-inch cubes
Place the soap in the top of the double boiler. Add three drops of the colorant and a pinch of mica. If you're using a fragrance oil, add it now. (Hold off if you're using an essential oil.)
Fill the bottom of the double boiler with water, place the top part on and put on the lid. Heat the water to boiling, then turn off the heat and let the soap sit for about 30 minutes. If you're using an electric range, take the double boiler off the burner. Test the temperature of the soap. You should never heat casting base above 160°F.
Gently stir the melted soap to evenly distribute the color, mica, and fragrance. (Stir gently so you don't stir up bubbles.) Adjust color and scent with fragrance oils if you want.
Pour the soap when it cools to about 140°F. If you're using essential oil to scent your soap, add it now, before your pour. Some bubbles will form through pouring, but you will take care of them later. Don't overfill the mold. Leave a little bit of room at the top so you'll have some leverage when you press on the back to unmold.
Let the soap harden in the mold for about 1 hour. (Deeper molds will take longer to harden; shallow molds will harden more quickly.) When you are certain that the soap is hard all the way through, unmold it and slice it into bars. Use a nonserrated table knife for a smooth surface effect, or a serrated knife for a lined surface effect.
Line up the bars on plain paper on a cookie sheet and let sit for 1 day. Wrap them in plastic wrap for storage.
If you unmold the block and it feels warm but looks like it isn't in danger of falling apart and making a mess, let it finish cooling out of the mold. Don't cut it though, or the runny center will come out, leaving you with a puddle on the counter and a hollow soap.
12 ounces clear soap base
2 to 3 drops soap colorant Pinch mica
1 teaspoon soap fragrance
Fill the bottom pan of the double boiler with water, put on the top pan, and turn the heat on high.
Cut the soap base into approximately 1-inch cubes. Place in the top pan. Add two drops of the colorant and the mica and the fragrance.
Put on the lid.
When the water in the bottom pan comes to a boil, turn off the heat and remove the pan from the heat. Let sit for about 15 to 20 minutes.
Take off the lid; the soap should all be melted. Gently stir to combine the mica and colorant. Check for color. If you want deeper color, add more colorant a drop at a time. (Add color conservatively. It is easy to add more, but you can't take color out. You can, however, add more clear soap to dilute the color.) Take the top pan off and wipe the condensation off the bottom.
Pour each mold to almost full. Spritz the surface with alcohol to eliminate any bubbles that formed during the pour. Let the soap cool.
After about an hour, release the soap from the mold by turning it over and pushing from the back. It should release easily. If not, let it cool a while longer. If you still have trouble, you may have a stubborn mold. Put the mold in the freezer for 5 minutes. The soap will most likely contract enough to be pushed easily out of the mold. For storage, let the soap sit out for a day, then wrap with plastic wrap.