If I were marooned on a deserted island, could I make soap?
January 13, 2015 8:51 AM   Subscribe

If I were marooned on a stereotypical deserted island (like Benjamin Gunn or Gilligan or in Lord of the Flies), would I be able to make soap and, if so, how? Assume I have access to standard deserted island stuff including coconuts, wild boars, fish, fresh and salt water, sand, palm trees, fire, sturdy vines, &c, and that I am handy enough to make spears and stone axes. Note that I am looking specifically for answers on how I would make soap and NOT for alternative methods of cleaning (I assume I could just scour stuff with the sand but I want soap).

1. What materials would I need?
2. What equipment would I need and how could I make it? If necessary, I might have the wreckage of a boat or plane but I'd prefer only materials from the island itself (hollowed-out tree stumps, for example).
3. What would the process be?

As a bonus, would I be able to make lotion? I assume my skin would dry out from all that swimming and whatnot.

Thank you for your responses.
posted by Mrs. Pterodactyl to Grab Bag (20 answers total) 15 users marked this as a favorite
Lotion: any sheep on your island? Make a knife, cut the wool off, spin it using a drop-spindle, knit some things. Your hands will love the lanolin.

Alternately: kill the boar and render the fat into lard. That'll work for lotion, as well as candles and food and other things.

The pioneers would make lye from wood ashes, as explained here. Once you have your fat (lard or beef, if there are cows on your island) and your lye, you can make soap.
posted by Melismata at 8:58 AM on January 13, 2015 [2 favorites]

Wood ashes and fat. Use coconut oil for lotion. Bonus: you smell like an Almond Joy.
posted by Johnny Wallflower at 8:58 AM on January 13, 2015 [6 favorites]

Soap is easy: fat plus ash. You'll need boar fat or coconut oil, plus ash from your cooking fire and some sort of crude cooking container.

Coconut oil all alone would be just fine as lotion.
posted by ssg at 8:58 AM on January 13, 2015 [1 favorite]

Well my understanding is that soap used to be made using rainwater and ashes (according to wikipedia). So if you could create fire and the island got rain, I assume you could use the fat from say a boar which we're assuming on there and mix that in a container. Looking it up at the cold process it seems that the issue is getting your saponification ratios right which I assume would be trail and error unless you keep a laminate card on you at all times.
posted by Carillon at 8:58 AM on January 13, 2015

Primitive soaps were made from potash and animal fats, so it wouldn't be much of a problem to make on a decently stocked island. You'd already be burning wood for fires - soaking the wood ash in water would create a potassium hydroxide solution (lye, basically). Not sure if making coconut oil is possible with primitive tools, but rendering animal fat is pretty trivial if you're already hunting and trapping for food. Mix together and you have soap.
posted by backseatpilot at 9:01 AM on January 13, 2015

As a hobby soapmaker, I can tell you you could use tallow or coconut oil, and lye (sodium hydroxide) which I understand can be extracted from ashes. However, these things need to be mixed in fairly precise proportions to make working soap that won't abrade your skin with lye, but will still clean. You mix the lye solution with oils, pour it in a mold (hollowed out coconut? Hammered together planks?) and just let it sit and react for 24 hours (this is called saponification). You can learn more about this by googling 'cold process soapmaking'.

I'm not sure how concentrated lye extracted from ashes is, but lye purchased from soapmaking suppliers can cause some unpleasant chemical burns if you don't use gloves etc.

Lotions may be more challenging, they are oil suspended in ~80% water, so you need an emulsifier to stabilize the mixture and an antibacterial agent or it will go rancid fairly quickly without refrigeration. If you are already extracting coconut oil somehow, you could just use that straight.
posted by torisaur at 9:01 AM on January 13, 2015 [3 favorites]

Oh, and a drop-spindle = any weight at all, such as a rock, that allows you to tie the wool on it securely.

Duh, coconut lotion, that is the obvious answer!
posted by Melismata at 9:03 AM on January 13, 2015

Response by poster: Thank you so much for all the answers so far! Please assume that I have a very small degree of knowledge and a desire for great specificity, so if you tell me to "render" the fat what exactly does that mean? If I have a dead boar, how do I get the fat off? (I do have a stone knife or cutting tool -- do I just cut it? How do I cut fat off a dead boar?) I will stop threadsitting but seriously, I would like VERY, VERY specific directions and I don't know anything about butchery or chemistry.

The more like a step-by-step guide is the more appreciative I will be. Imagine I am currently on a deserted island and you are giving me life-or-death soapmaking instructions by radio broadcast.
posted by Mrs. Pterodactyl at 9:10 AM on January 13, 2015 [5 favorites]

How to make African Black Soap. I think most of the ingredients would be on a theoretical tropical island. Maybe swapping plantain skins for palm tree leaves. Making the palm oil would be a pain, but doable, with I believe a simple but strong press, & it would be a useful for cooking with as well. Or you could make a hybrid version using rendered animal fats too I suppose, which would be good enough for trapped on an island use.
posted by wwax at 9:12 AM on January 13, 2015 [1 favorite]

How to render fat. Note that the instructions assume that you've already chopped all the fat off the animal - which you could do in the process of butchering it, which I assume you would be doing anyway for food purposes. So it'd be like:

* Take your dead boar.

* Skin it and cut it into pieces.

* Take each piece and cut the big fatty bits off and put them in one pile; then put the meat bits in another pile.

* You would be left with the meat bits that you can eat. And a pile of fatty bits which you can render into a pure fat.

All "rendering" means is, you're cooking away the tiny trace bits of not-fat which may still be attached to the fat, so it can be used for all your fat-requiring purposes.
posted by EmpressCallipygos at 9:20 AM on January 13, 2015 [2 favorites]

It seems like you should be able to make coconut oil, too - How to Make Virgin Coconut Oil. Regardless of which fat you use, you'll need some kind of cooking vessel and a cutting tool, and for coconut oil you'll probably also want some kind of grinding mortar/pestle situation.
posted by mskyle at 9:56 AM on January 13, 2015

Rendering: boil the pieces of fat in water. The stuff that collects on the top of the pot is your rendered fat. When it cools down, it becomes semi-solid.
posted by musofire at 9:57 AM on January 13, 2015 [3 favorites]

You don't mention why you want to know this, but presuming you are interested in the slightly broader topic of "castaways attempting to recreate the trappings of civilisation" you might dig Jules Verne's The Mysterious Island, a kind of prequel to 20,000 Leagues Under the Sea, in which he sticks five survivors of a hot air ballon wreck on a tropical island, including an engineer, and basically has them attempt to recreate the 19th century's advanced technology step by step. It's science fiction, but trust me, it's really heavy on the science part, with enough light plot tossed in at intervals to keep the thing nominally qualified as a novel. It discusses how to make soap, gunpowder and candles starting from raw materials, and that's just the beginning. Free for dowload in Project Gutenberg.
posted by Diablevert at 10:19 AM on January 13, 2015 [10 favorites]

Colonial Soap Making: Its History and Techniques

The key bit:

In another large kettle or pot the fat was placed with the amount of lye solution determined to be the correct amount. This is easier said than done. We will discuss it more later. Then this pot was placed over a fire again outdoors and boiled. This mixture was boiled until the soap was formed. This was determined when the mixture boiled up into a thick frothy mass, and a small amount placed on the tongue caused no noticeable "bite". This boiling process could take up to six to eight hours depending on the amount of the mixture and the strength of the lye.
posted by gimonca at 10:41 AM on January 13, 2015 [1 favorite]

Oh, and the bit right after:

Soap made with wood ash lye does not make a hard soap but only a soft soap. When the fire was put out and the soap mixture was allowed to cool, the next day revealed a brown jelly like substance that felt slippery to the touch, made foam when mixed with water, and cleaned. This is the soft soap the colonists had done all their hard to produce. The soft soap was then poured into a wooden barrel and ladled out with a wooden dipper when needed.

To make hard soap, common salt was thrown in at the end of the boiling. If this was done a hard cake of soap formed in a layer at the top of the pot.

posted by gimonca at 10:43 AM on January 13, 2015

Article does mention, too, that getting the lye solution to a good strength involved a lot of guesswork.

(I make cold process soap at home--made some this last weekend!--if your desert island person has access to a scale and industrial lye, say from a fortuitous plane crash or shipwreck, they can do all sorts of things.)
posted by gimonca at 10:48 AM on January 13, 2015

If you were in the northeastern Pacific, yet another fat source might be the candlefish.
posted by gimonca at 10:51 AM on January 13, 2015 [1 favorite]

The BBC series Rough Science (5 scientists on an island) covered this scenario. They made a liquid soap using wood ash to make potassium hydroxide and a mixture of coconut and olive oil for the fat.

There are a few more details here, but the recipe given at the end doesn't cover working from the raw materials.
posted by boffin police at 11:05 AM on January 13, 2015 [1 favorite]

Once you have ashes, you let them soak for a day, and you know when the lye is ready because a raw egg will float in the middle of the water.
posted by spunweb at 1:26 PM on January 13, 2015

And by middle I mean in the middle of the container-- water above and water below. I think you can use a potato or taro root instead of the egg... Or actually a feather. The little tiny hair like bits of the tuft of the feather will dissolve when the lye is ready for soap making.

Source: a surprisingly intense experience in Girl Scouts.
posted by spunweb at 1:30 PM on January 13, 2015 [3 favorites]

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