CAELUM – The Engraver's Chisel – Recipe, process notes, guessing game resolution
In my garden, I am plagued with a nasty weed that doesn't forgive you sloppiness over the years –
maple (#1, 1). In less accessible corners, or if you “just let it grow”, they'll grow until woody enough to be cut into viable
firewood logs (#1, 2).
Campfire time! (#4, 2 and #7, 1). Of course I collected some of the
ash (#7, 2). After
sifting it (#9, 1), I was surprised how well the distinct “generations” of ash harvest (with different charcoal content) were forming these layers in the collection containers.
In the meantime, it
rained (#3, 2), and I collected enough rain water for the whole further process. This had NOTHING TO DO WITH THE FACT that I was running low on distilled water once again, lol. I used it to dissolve the ash. Ash, as the inorganic residues of burnt plants, is mainly comprised of the carbonates and oxides of calcium and potassium. Lucky enough, maple is hardwood and an excellent source of potash. I extracted 105.6 g of ash in four steps, each one leeching soluble salts from the filter cake of the previous stage. After filtration, I got a clear, slightly yellow solution of
specific gravity 1.027 (#9, 3; more about yield later on), which is
strongly alkaline (#9, 2) – time to strap on safety equipment!
I was tempted to use the strained off charcoal as a colourant by itself, but decided against it – but I still have it, patiently awaiting further usage.
I can't know for sure how reactive the lye really is, or if it had pulled carbon dioxide from air to form potassium carbonate that pretends a too high lye concentration, and isn't well suited for soap making. The resort is
caustification: scavenging carbonate with calcium hydroxide (slaked lime), converting potash (potassium carbonate) to “caustic potash” (potassium hydroxide). Once an excess of slaked lime is added, it will form a whitish
sediment of calcium carbonate (and unreacted hydroxide) that settles
(#11, 3) and eventually gets filtered off
(#13, 1).
Now I'm left with 457.3 g of a caustified potash lye with a final SG 1.025, and it's math time! Per a
KOH density calculator I concluded that, if all the dissolved solids
were KOH, I'd have 14.13 g KOH at a concentration of 3.1%. Eventually, numbers to plug into a
lye calculator!
Since the concept of making things more complicated than absolutely necessary is totally unknown to me, I opted for an untested variation of
GLS creamy liquid soap recipe, and replaced most of the ingredients with ones more up to the garden theme: HO
sunflower oil (in lieu of
Helianthus annuus, photo
#11, 1 shows the
Helianthus tuberosus as growing in my garden), castor oil, and (as a colourant), 1%TOM
paprika kernel oil (#3, 1). As a replacement for cocoa/shea butter and stearic acid, I used the more temperate-climate-appropriate
canola wax (#13, 2).
I started off with the sunflower, canola, and half of the castor. I knew I had a lot of
water to boil off (#14, 1) until the reaction would jump off and give some
early HP batter (#14, 2). As suggested earlier, the assumption of pure KOH solution wasn't particularly accurate, and even though I left out some of the castor oil, I ended up with all lye used up and constantly failing clarity test.
You might intervene and remark that I still had noticeable amounts of calcium in there (solution saturated with calcium hydroxide from the caustification step), and that calcium (soap scum) would be water insoluble. Heck yes, but I even made a concentrated EDTA solution to dissolve any calcium deposits, and still the clarity test was turbid, indicating that indeed unreacted oils were present.
In an emergency, I resort to commercial KOH. Added a minute amount along with the paprika kernel oil (lol, the
third time in a row using it to colour my monthly challenge soap; only today I eventually finished up that tiny bottle of red-glowing goodness). The clarity test was positive after mere minutes, and so was the zap test, i. e. guessed just the right amount of extra KOH.
The soap was not entirely clear during cook due to stubborn air bubbles (that weren't even possible to be broken down by spritzing with
kirschwasser (#4, 1)); it turned out that I just had waited much too long to add the decadent 60%TOM of extra glycerol. This helped with fluidity in the hot state, adjusting viscosity via dilution/evaporation, and as a film formation/burn-in prevention. Upon cooling the precipitating stearate from the canola wax lent the soap its
silky appearance (#14, 3) somewhere between peach and orange marmalade.
The soap has “just the right, syrupy” viscosity for a LS, is mild yet cleansing well and with a decent lather (though no lauric oils!), and has a barely noticeable, slightly fruity odour to it. Unfortunately, the potassium/calcium stearate/air cloudiness isn't in a stable dispersion state, but tends to sediment over the days at the top, and leaves a clear, orange-red LS underneath.
By the way, the slightly esoteric-sounding name of the soap in fact has some “astrological” meaning: Some months ago, I have started to name my soaps by stellar constellations, for easier organisation of my notes and curing rack(s). I took the
IAU official list of constellations, sorted them from north to south, and now I'm picking names from this list. Lol, hard to tell that even these 88 names are used up in due time, when I'm already
that much south on the sky map that the constellation doesn't even fully rise over the horizon in my latitudes?
Caelum is the Latin name for this young, non-classical constellation without much astronomically interesting stuf going on there. Its main quality is that it exists, and is the last-but-27th entry on a list that should have lasted me “forever”
Regarding
yield of wood ash-based KOH lye:
I used slightly above 100 g of ash – the exact amount is not so intersting, since highly dependent on the content of residual charcoal. The solution after extraction but before caustification contains mostly potassium (but also minute amounts of sodium) salts: carbonates, hydroxides, sulfates, etc., in unknown relations. For the sake of simplicity, I'll neglect Na for the moment.
After caustification, I'm left with dilute KOH solution, saturated with Ca(OH)₂ and CaSO₄ (each no more than 2 g/L). Carbonate and excess sulfate has been precipitated to lime and gypsum. When I neglect these, I'm left with a KOH yield of about 13% m/m from the ash. Judging from the amount of charcoal that is included in this weighing, I'd honestly expected far less. Well, as it turned out, I also
got less than that. I had initially planned to use 30% castor oil, but leaving out 15% of the original oils already exceeded the lye capacity, so I have
overestimated KOH yield by about 15% from some unknown reason.
A major source of uncertainty entered the equation via the density reading by hydrometer. It is one made for urine investigation (it turns out that it might well be 100 years old). In its handling it actually appears decently precise, and I even have successfully tested it with a sucrose solution. The only other thing I can imagine is an incomplete caustification reaction, i. e. still a fair amount of potassium carbonate present in the final lye solution. But then I would have expected the solution to foam up upon addition of acid – which it didn't either. Only a careful titration could tell more, but you must know I am a lazy person (at least as soon as it comes to cleaning burettes after titration).
So what. The only “issue” with this was that now not 100% but only some 85% of the final potassium was “home-grown”. I now have this experience, as well as another 400 g of ash (and some more wood to burn) for the “bad times” to play around with. And a beautiful, creamy, mild liquid soap
filled back into the kirschwasser bottle (#15) and screwed – thanks to standardisation craze – with the very dispenser cap that once decorated a bottle of rice vinegar.
Enjoy!
It's a towel with owls sitting on a line! I discovered it a few days ago while clearing up, and thought it'd be a great “signature backdrop” for me.
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