Sunday, 9 November 2008

Putting that education to use

So what crafty hobby should someone with a Masters degree in chemistry have? I mean, knitting's all well and good, but doesn't really cut it on the science front (although Cassie has written recently about knitting scientists and other mathematical types - also, please go and do her questionnaire on knitblogging) and I felt I needed something with the ability to write an equation and a bit more potential for dangerous chemical burns. Cold process soap making seemed to fit the bill, so hell, why not? You all know what you're getting for Christmas now, and indeed birthdays, forever.

I armed myself with two books before I started, it always being helpful to be informed, and besides, I had no idea what ingredients to order. The one recommended by this website was The Soapmaker's Companion by Susan Miller Cavitch. This is a very comprehensive book, from first steps through to the actual science (with bonding diagrams and everything). I read it cover to cover, but don't find it terribly well laid out. I think I need to apply some judicious sticky labels down the side. The other book, The Handmade Soap Book by Melinda Coss, is far simpler, and easier to follow, but not as informative. They work very well together though. That and a spreadsheet I just had to make myself for the saponification values, being the uber-nerd that I am.

Soap making is rather dangerous, as it involves NaOH, otherwise known as sodium hydroxide, caustic soda or lye. This stuff can burn through flesh, disfigure and blind. You know, I don't recall being particularly scared of it at university, where we threw noxious stuff around the lab with impunity. Perhaps that was the general feeling of immortality that every late-teen has, or perhaps the comforting presence of the lab techs who I'm sure would have known what to do in the event of severe injury (and I only ever saw one bad chemical injury during my studies, although many more cuts on broken glassware). I used to come home with my clothes full of little holes, but miraculously not my flesh. These days, I have far more fear, and therefore approached the lye with caution. In all seriousness, this is bad shit, people.

Because of my course and habit of never throwing anything away, I was already kitted out for protection when I embarked upon the practical session this weekend! This is how you would have found me in the kitchen on Saturday afternoon:

And with a little knowledge of acids and bases, I got out my bottle of vinegar (normally used as fabric softener in this house) to splash in case of alkali burns. Mortal enemies:

The process for making soap, or "saponification", involves the sodium hydroxide turning the fatty acids found in a variety of fats and oils (and, oh, skin, hence those burns) into glycerin and a sodium salt which we normally know as "soap". If you look on your proprietary soap and see something like "sodium tallowate", "palmitate" or "stearate", that's your salt. Indulge me for a second:

C3H5(COOR)3 + 3NaOH --> C3H5(OH)3 + 3NaCOOR

OK, OK, no more of that, I promise. The actual process is relatively simple, assuming you get the amounts right. The amount of lye needed depends on the exact types of fatty acids (those COOR chains) and every kind of fat and oil out there has many different types in different proportions, leading to different lathering/cleansing/conditioning properties. So you can either follow a recipe for the amount of lye, or use some nice numerical charts from the books. I followed a recipe for batch 1 but have now made that spreadsheet I mentioned to work it out for my own proportions of oils.

The fat is by far the most innocuous step. My first batch was to be made of coconut oil, palm oil and olive oil. The first two are solid at room temperature so have to be melted. Here was my pan of fat before melting:

Heh, no I promise I didn't go all Fight Club and source bloodied human fat from the local liposuction clinic. The red colour is because I had steeped the olive oil in chopped alkanet root first. This is a natural dye, acting a bit like litmus paper. It's red in acid, but turns a pretty blue-purple in alkaline conditions such as soap. Seeing as I was scenting this first batch with lavender (being a nice cheap essential oil if this went wrong), it seemed appropriate.

Whilst the oil is cooling back down to around 40C/100F, you prepare your lye by dissolving this very innocent-looking stuff in water. Do not confuse it with sugar.

The mixing with water is highly exothermic (heat generating) so that also has to cool. Mine peaked at about 70C when first mixed, with noxious white fumes given off, and took a little while to cool. Here's where the chemistry training came in useful, with it having been drummed into us for years that you add most reactive to least reactive, never the other way, ie base to water not water to base. That's because if the first drops of water hit that base, there'd be a huge exothermic reaction which is dangerous, whereas the other way round the excess water will quench it. Similarly you add the lye to the fat, not vice versa, later.  The books mentioned doing it this way round, but not why.  Given I like ignoring instructions, I might have done it the other way, had I not known better.

So here were the two liquids, pre-mixing:

The rest all went pretty quickly so no photos. Lye gets added to the oils, and the mixture is then stirred vigorously. I used an electric whisk. This did cause a bit of splashback and I have some tiny red marks on my face from it, and man, they stung - I soon learned to use a pan lid as a splashguard. After 15-20 minutes, when you drip the liquid back into itself, you can see a faint mark on the liquid surface. That's called "trace" and means it's time to add other stuff, such as scent, then pour it into the molds. Note that if you rush this bit, the soap can separate back out into caustic soda and fat, leading to a rather nasty chemical peel instead of nice, fluffy bubbles. I used silicone bakeware (love this stuff) which is non-reactive (teflon or aluminium being bad choices here) and easy to unmold again. I layered dried lavender flowers into the bottom then poured in the soap. Here it is, poured into two loaf tins and some overflow yoghurt pots, as it made more than I thought it would, then wrapped in clingfilm against contamination:

Look how purple the alkanet root had gone! They are then wrapped in towels for insulation, and left for a day to happily react away, generating lots more heat as they go. I kept peeking, of course. Who wouldn't?

This evening I got to free them from their molds, which is important to do whilst the the soap is still soft enough to cut into bars. It then gets to sit and cure further for another four weeks, until it's mild enough to use. Here's the cut soap, which by this time was a pale lilac:

Pretty! So that seems to have worked. I started another two batches tonight, one floral, one rather more manly at my darling's request - he is ever so forbearing of my whims, although did suggest that I could do with a shed.

Fingers crossed it is fully cured in time for present-mas!

1 comment:

stash haus said...

Lucy - you never fail to amaze and surprise. I'm much more timid (having come close to failing chemistry and breaking more beakers than anyone I know). I guess I'd be willing to try this in a classroom - with someone other than myself in charge. But the end result is lovely. When will we have scratch n' sniff computer screens?