I do it every few months, and think nothing of it - except that the whole process is a rather satisfying one.
Soap (cakes of it, that is) is much wasted. Hotels provide small tablets of usually inferior soap, which may be used once or twice and then thrown away. At home, when we have come at last to pieces so small that they are useless, we, too, throw them away. I don’t, and have not done so for years.
In my bathroom is a drawstring, net bag, at one time used, possibly, for something like Chinese garlic bulbs. Into it go the odds and ends of used soap – all to be enjoyed again later in a much larger, blended form.
Here is what you do.
Save meshed, plastic bags – the kind used for shallots, garlic, plums and much else.
It is wise to coat the surface on which the following operation takes place with a few layers of newspaper.
Take your used pieces of soap from the (bathroom) storage bag, and put them, higgledy-piggledy, in a meshed bag, cutting large pieces, if any (they might be cakes of soap that you did not like particularly and have become dried and cracked), into smaller pieces. Tie a knot in the bag, or close it with a freezer bag wire tie, to keep the pieces as close together as possible.
You will need a press of some sort. I use a squeezer for half oranges – which is ideal. You could use the like, or a deep bowl, or perhaps a section of tubing – like plastic drainpipe. In the case of something like a bowl or pipe it will be necessary to have a disk that you will press down on to the soap when it has been softened by steam. A potato masher would do.
You will also need a plastic bag, like a freezer storage bag. This will stop any very soft soap from escaping the press.
Now put an inch or two of water in an appropriately sized saucepan (i.e. a deep one to prevent soapy water from bubbling out over the saucepan and on to the stove). On the saucepan place a metal colander. Put the tied bag of soap bits in the colander and heat the water beneath to a low, tick-over boil.
To concentrate the resulting steam, rising from the water and passing up through the colander holes to the bag of soap pieces, place a saucepan lid over the bag to fit the inside of the colander.
Prod the soap pieces every so often (with the point of a knife or skewer) until they become soft (some will be softer than others, with some transparent varieties sadly melting into the water below).
When you think that all the bits of soap will cling together (some may still be fairly firm), lift out the bag of softened soap and drop it into the freezer bag (rolling down the sides of the bag beforehand to facilitate the operation). Be extra careful in doing this as the soap will now be very hot and can cling and scald.
Do not tie up the freezer bag, as air must be allowed to escape from it.
Now press or squeeze the meshed bag within the freezer bag until the bits of soap unite and take the form of your press and future cake of blended soap.
Allow the bagged soap to cool for a few minutes. Then extract the meshed soap from the freezer bag.
Using scissors, cut away the mesh bag from the pressed soap, and put the hot cake of soap on to a plate.
There will be rough joins and crevices in the new cake of blended soap. Bits of soft soap will cling to the bag mesh.
Prise away the soft soap bits remaining in the bag’s mesh and use it to fill the cracks and holes in the large cake. Again, be careful of the hot soap. Do not worry about any final odd protrusions or unevenness. These will disappear with use.
Allow the soap to cool. Keep it for several days, or longer, before using it.
The chances are that you will now have a large lump of lovely soap that you will use and enjoy - luxuriantly.
Washing up afterwards is easy. Everything used is soapy.