Made tons of the stuff over the years.
First, ye take a bunch o' fat and render it doon. (or ye can buy dripping frae Sainsburys - it's the same thing)
Get yesel' three buckets (plastic ones frae B&Q will do). Put wee holes in the bottom o' one o' them. Get yesel' wood ash frae the fire. It has tae be frae hardwood, an' nae ither rubbish has tae hae been burned. Put some straw intae the bucket wi' the holes. Fill the bucket wi' ashes. If it disnae fill right up, keep it till ye hae mair ashes.
Put twa bits o' wood ower one o' the ither buckets so's the one wi' the holes can sit on top o' it. Noo gather rain water in the third bucket. Fresh stream water is good an' all, but dinae use tap water if it has chlorine in it.
Slowly pour the water ower the ashes and let it trickle through intae the bottom bucket. Once a' the water is poured in, let it sit until there's nae mair drippin' oot o' the bucket wi' the holes.
Check tae see if the lye (that's whit the resulting liquid is called) is strong enough. Put a fresh hen's egg in the bucket. If it floats, the lye is too strong - add some water. If it sinks, the lye is too weak - pour it through the ashes again. If it just sits there in neutral boyancy, it is just right.
Noo put the drippin' an' lye in a big pot and put it on the fire. Stirr wi' a big wooden paddle while the mix heats up. It'll separate oot an' look an awfie mess, but keep stirrin' a' the time. After a while, as it boils the mix will coagulate into a thick mess. Keep stitting more noo or it'll burn. Stir it till it reaches the consistncy of mashed taties.
Tak' it off the fire and scoop the mix intae boxes lined wi' old newspaper. Press doon intae the boxes then set aside for a couple of days to set.
After a coule o' days, turn the soap oot o' the boxes and cut intae bars o' soap. Place these somewhere dry but not too warm where the air can circulate roond them Leave them for six weeks tae cure. Then ye' can use the soap.
That's granny's recipe for soap and is how it would have been made in times before the convenience of shops.
What happens is this. The water passing over the ashes leaches out the potassium salts. The straw acts as a filter and an alkali solution not unlike caustic soda ( but much weaker) emerges. Because fat is acidic, the lye reacts converting the fat to soap. However it takes six weeks for all the lye to properly convert and if you can't wait, you need to do the tongue test. You take one of the bars of soap and touch it on your tongue. If it tingles, it's not ready. Leave it for more curing time.
You can add essential oils and emoluments or exfoliants right at the end and stir it in if you like, or you can just keep it natural.
I like to put anise oil in and some gravy browning. I put gravy browning in half the mix and twirl the two colours together like a camo pattern. The anise scent covers my human scent and I have used it to get really close to deer in the past. I call it hunter soap.
This is all straight off the top of my head. I'll have to look in the book and get you the quantities of fat to lye. I'll add the proper recipe later.
Eric