I will start with the absolute basics, then include a few more ideas later on. If you already make soap and are just looking for new ideas, you might want to skim over the basics and head to the end!
Just a note: Melt and pour soap could be considered a 'cheat's' way of making soap, as you purchase pre-made soap base, melt it and add things to it. I like it because it is ideal for a small kitchen, very forgiving and easy to be creative with. It would be an ideal project for kids, though under supervision only - the molten soap can get very hot, and before melting it usually needs to be cut up with a knife, so please be careful!
An inventive example of what you could do with M&P soap can be found here.
Step 1: Gather ingredients and equipment.
Melt and pour soap base, either clear or opaque, or both - I tend to get mine in very big blocks on ebay. Beware, it must be M&P soap base, most ordinary soap won't melt. I learned this the hard way so you wouldn't have to!
Soap colouring - ebay again. Be sure to get the water soluble colours if you are using clear soap.
*There are several specialist soap making shops online - so far ebay has always been cheapest for the soap base and colouring. You might find things cheaper elsewhere if you are prepared to shop around a bit. *
Cosmetic grade scent or essential oils - I buy essential oils from places like health food shops. Soap making sites stock special scents but essential oils are cheaper and more natural!
Surgical spirits - try your pharmacy, I got mine from Superdrug. I believe it is known as rubbing alcohol in the US. I have also read that you could substitute witch hazel, though I haven't tried it.
A microwave - You could do this in a double boiler on the stove if necessary, but that would be a nuisance!
Microwave safe container to melt the soap - I picked up a couple of microwave pots on sale in a local thrift store for about a pound. A microwaveable plastic or glass jug works well too. You really want that pouring spout!
Something to stir with - I used some pieces of dowel rod we had lying around.
A small spray bottle - try the travel section of your pharmacy. I got mine from Superdrug.
A mould - this needn't be a specialist soap mould, though there are plenty of them available on ebay and soap making sites. Any reasonably flexible container will do, as long as it won't melt too easily! Think cream cheese tubs, yoghurt containers, silicone ice cube trays etc.
Cling film - This soap does not like being exposed to the air, so wrap it fairly soon after it has set.
A chopping board and knife, or a grater - chopping or grating the soap base helps it melt .
A scale - this becomes less necessary as you learn to measure by eye.
If you buy the powdered colourant, you will also need some small dropper bottles (pharmacy again) and other small containers such as plastic shot glasses to mix it all up in.
Some people are fussy about not using the same piece of equipment for both craft and food, but this is soap for goodness sake! I am more concerned about getting a bit of old broccoli in my soap than having food taste funny. Just wash it well and you will be fine.
Optional - Things you might want to add to your soap to make it look pretty
Glass or plastic beads
Children's novelty pencil rubbers
Small soaps or pieces of commercially made soap
Buff Puff - Those scrubby things made of plastic-y netting.
Small plastic or rubber toys
Gold or silver powder
Any other non-organic, non-ferrous item you wish to embed in your soap. Don't be tempted to use anything that could react with water (e.g. dried flowers) as the soap has a high water content. It might look pretty now, but mould or rust in soap is not a nice idea!
This seems like a lot of stuff to buy, but really you can make do with the minimum to start with and add to your collection as you go along. The more expensive parts are the soap base, the colouring and special soap moulds. Everything else can be bought cheaply for a few pounds or less. If you keep your eyes open and shop around a bit you will find all sorts of things you can use, even if they are meant for something else entirely!
Step 2: Preparation
Measure the volume of your mould in millilitres using water and a measuring jug if you have one. You will need a similar weight of soap base in grams. I tend to measure by eye and have a small mould (eg shaped ice cube trays) standing by for any excess, but it is initially difficult to guestimate the amount of soap you will need.
Chop up your soap and weigh it, then place in your microwave proof container. If you have the patience you could grate it - small, even pieces melt easier than big, uneven pieces.
Step 3: Nuke it!
Add colouring and scent and stir it in. The amount of colouring will depend on the depth of colour you are trying to achieve - if using clear soap in a white container the colour will seem deeper than it actually is. You will learn what works for you!
Be careful with strong essential oils like peppermint or tea tree, if you use too much they will sting when used on *ehem* sensitive areas. Start with a couple of drops and add more if needed. The soap will have a slightly stronger scent when it is used than when it is molten. Always add your colour first so the soap has a chance to cool slightly before adding essential oils - if the soap is too hot you will simply evaporate them. This also goes for re-melting soap to which you have already added scent, you might need to add a little more.
Step 4: Pour and wait!
After pouring and spraying, leave the soap where it is to set. Try not to bump it for at least half an hour, as the soap forms a custard-like skin on top which will wrinkle if you bump it. Again, it will still work, but looks a bit odd. I find that even stepping heavily on the wobbly floorboards can cause this problem, so be careful and place your mould in a safe place before you pour the soap.
Step 5: Finishing up
To de-mould the soap, tip the mould upside down over a suitable surface, and gently flex your mould and push the base. If it is properly set, the soap should pop out quite easily. If not, leave it a while longer or try the freezer trick. A complex pattern in your mould will make it more difficult to remove.
Admire your soap, then wrap it in cling film. You don't need to do this immediately, but certainly within a day or two, as the soap can 'sweat' if left out for too long. If you like, you can make a fancy label for it.
Step 6: Making it look good.
When embedding anything, or making layers stick, spritz well with surgical spirits. The only limit is your imagination!