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waste ash from forge operations


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Hi. Quite a while back, someone posted something about recycling ashes from the forge to avoid dumping them in the waste stream. Maybe it was Ice Czar.

I have begun to explore this possibility, and found out, like most good ideas, it is more complicated than it sounds ;). In the old days, these ashes were useful for making two kinds of product, soap and potash. The soap sounded like an interesting proposition, since there are lots of articles explaining its production from ashes on the Internet. A lot of these articles look very practical, but there is always the counter-Einsteinein cry, YMMV!

So, before beginning an expensive large scale operation, it seemed more reasonable to do a small pilot study. Besides, there would be no credibility if I just presented folks with a bunch of web page addresses, rather than some real, cold, solid, hard, defensible, practical, up close, etc, etc, etc, ..., results. I took about 2/3 of a gallon of fluffy white ash from burning charcoal. It contained a few small unburned charcoal pieces in it. It was covered with water to about 1/2" above the top, and left to leach for two weeks. It was stirred thoroughly once per day.

At the end of the period, I went to the chicken barn and asked the animal husbandry manager on duty for a few chicken feathers. It is amazing how tightly those chickens hold on to their feathers when you would like a few ;). Dipping one feather in the slightly discolored liquid, it was noted to *not* dissolve, even slightly. This test is a well-known one to see if the potassium lye has reached the required strength for soapmaking. I am suspicious that if it was left for another two weeks or two months, it would not reach adequate strength.

There are a couple of guesses for the failure of this tiny pilot study. The most likely is that the ash is not suitable because of how it was generated. Upon further searching, it was noted that potassium hydroxide is not naturally present in the ash, but it is produced in a classic metathesis reaction between potassium carbonate and calcium hydroxide. The latter comes from the calcium carbonate which has been roasted by long contact in the fire to quicklime. And herein lies the main problem, not enough residence time in the forge. Ash which is produced rapidly drops to the cooler portion of the ash dump and is blown and discarded. Not much time to roast out. I did some experiments on roasting limestone, and it takes awhile. That's why America's first patent was so important.

Am I on the right track? Does anyone have any experience with this technology? Would I make a good practical partner to the more theoretical Ice Czar? :)

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I think it was Ice Czar who pointed out that charcoal scraps were beneficial in the garden.I had known that wood ashes worked sort of like diluted lime and helped control soil acidity. The wood ashes also puts a small amount of nutrients in the soil..a quite safe and natural fertilizer.

I only recently learned of the benefits provided by the bits of charcoal.It 'lightens' heavy clay soils in much the same way as peat moss or even compost.

I've never made any soap, so I can't comment anything useful on that subject.

As far as coal ashes are concerned, all the gardening books I've ever read warned not to put coal ashes in the garden,........and I never have. But I do offer this observation...........that around old coal piles or old ash piles I often see rasberry briars or walnut trees.
Around here, for more than 50 years, coal was the fuel of choice for home heating. Almost every house had a 'coal pile' somewhere in the back yard. The ashes were usually discarded somewhere nearby.
There's something( probably sulphur), in coal, which rasberries and walnuts like.

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All the reading I have done mentions hardwood ashes as being used to make the lye basis of soap, commonly from wood burning stoves or fireplaces. Your charcoal ash was probably too fine and too well consumed to yield a proper strength of lye.

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I know I'm straying far from the subject of making lye soap, but did you know that pigs will EAT coal?
It used to be common practice among old timers to throw a couple handfuls to their pigs occasionally.
I no longer remember if the coal was meant as a mineral suppliment, or as a 'dewormer'.
Not only will they eat it.......They like it!
There's nothing quite like seeing a 500 lb. hog munch a fist-sized lump of coal as if it were a piece of candy.

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hmmm....my ears were burning :P

terra petra (Intentional use of charcoal in soil) ;)

Am I on the right track?

from here it looks like your on a different track :P

caveman chemistry

Lime has two advantages over potash. First, it is a stronger base than either sodium or potassium carbonate. Second, unlike potash, it can be produced in large quantities. Remember: a lot of wood produces a little ash and a lot of ash produces a little potash. But limestone is a very common stone. We can quarry it and produce lime on a grand scale.

then goes on to recommend employing lime and soda ash, which isnt what I originally proposed but is certainly viable

While lime is more alkaline than soda ash, when reacted together they produce a stronger alkali than either of the two separately.

as to why your pilot program for lye water might have failed
charcoal stock was hardwoods? this is very important

you used soft water? (rain water) containing few or no calcium or magnesium ions? also important.

Then typically unless youve got some really high grade woods, you have to boil the lye water till you can float an egg, then you have "lye". At which point its on to completely boiling it off to potash, then toss it in a kiln to reduce it to pearlash.

the point of my orginal post wasn't about the production of pearlash, so much as the use of the waste stream and waste heat to a useful end, a by-product as opposed to a product.

The First Patent

Hopkins's key advance lay in burning the raw ashes in a furnace before they were dissolved in water. This second burning resulted in much greater carbonate formation, apparently because the free carbon in raw ashes (which partly accounts for the black color) was more completely oxidized and because of exposure to concentrated carbon dioxide gas from the fire.

Would I make a good practical partner to the more theoretical Ice Czar?

oh definitely :P Im still ignoring my gasifier at this point. Its spring and that means the house remodel is the first priority. Personally Id boil down that lye water so you get an idea of what your wood stock is like. Then try a few other sources. Will help with whichever process you pursue. ;)
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I know when my late father was an army medic one part of his training involved how to make medical supplies from almost nothing. One trick was to put a filter of grass, sticks etc. over the drains to the kitchen and thus retain the grease. This was then turned into soap but I forget where they gleaned the alkali to do it. It was certainly from some waste product. Could have been ash.

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Hi. That Caveman Chemistry site was certainly interesting, but it wasn't quite complete for the purposes of the discussion. The Caveman Chemistry page gives a method for producing lye by mixing potash or soda ash with slaked lime to perform the metathesis reaction. Some of the ash lye recipes mention addition of lime to the ash as it is being extracted. Can't hurt. But, other sites say that there is enough lime generated from the ash itself to perform the reaction. Wood ash is nearly 1/2 calcium carbonate, and when it is in contact with the fire for long enough, it becomes calcined to quicklime. When I was a kid, I borrowed a chemistry book from the library and it told how to calcine limestone to quicklime over a gas stove flame. I used an old tin can and filled it with crushed oyster shells. The paint burned off and I stunk up the whole house. My mom came running and asked what I was doing. I was afraid of a big punishment, but she looked at the book and said she had a lesson to teach me. I replied that I hoped it wasn't painful. She said, it would be, but it would teach me something valuable for the future. She went to search for something, and I feared that it would be a brush. In a short while, she returned with a small white smooth thin-walled dish. She told me that it was a crucible, and she kept it from lab in college. For tasks such as calcining limestone, it was more suitable than a painted tin can. I remember that we baked those crushed shells for nearly an hour on a full flame. The cast iron burner grate glowed a faint red, and the whole stove was hot. By then, she said that my pitiful little can would have burned through. We let the heated crushed shells cool, then dripped water to observe the classic hydration reaction. Nothing. She then looked me in the eye, and asked me what did I just learn. I was so frustrated; I didn't know what to say. She said, "I thought this might be painful, but it is a good lesson. You just learned that you shouldn't believe everything you read. Not even if it is in a library book. You will probably have to relearn this lesson, but it shouldn't be quite as painful later." She was right. She did not know it at the time, but she just predicted mine and others' abortive forays onto the web. Fortunately for us and other practitioners of the field, sanity checks of the literature are absolutely necessary to put nearly any of the literature into practice.

I should have been suspicious when the dry ash did not puff up as I added the water. One of the web sites telling how to make soap from wood ash said that there should be a visible reaction when the water hits the ash. I saw no such thing. It may be that I have just produced an impure mixture of potassium hydroxide and potassium carbonate. If this is boiled down to float a raw egg or a potato, it may or may not be suitable for making soap. I don't have the wherewithal to test the proportion of potassium hydroxide, and I don't even know if potassium carbonate will act in the saponification reaction as the lye does. I did borrow a pool test strip, and the liquid shows off scale on both alkalinity and pH. But this does not tell much, since potassium carbonate is fairly basic, and will show off scale. Furthermore, even relatively weak solutions of potassium hydroxide will measure in the 13-14 pH range, way off scale.

Hydrated lime is pretty cheap, and I may be able to get some on the farm, but it may be inconvenient. From the chicken feather test, this shows that lye in appreciable concentrations is not formed, and the alkalinity of the waste product is limited. All in all, this is not all that bad news. I have reviewed these findings with the farm horticulturalist, and it seems that the ash may be safe to mix in with the compost. So, in a sense, the project of diverting the ash from the landfill bound waste stream was successful. Of course, I could try the potato trick. Probably not worth a whole potato; just a piece. If it works, maybe add some junk fat to see if it saponifies. And, there still is the task of diverting the fat from the waste stream, since when we slaughter the hogs, the skin fat goes to waste. Maybe just have to bite the bullet and use store bought lye. We could certainly use some decent soap at the blacksmith shop. All the fellas get so dirty in there.

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Well coming from the hills my great grandmother used to make her own lye soap. Had a large wooden barrel that they would dump the woodstove ashes (hardwood) in till it was full then pour the water through several times to get it more concentrated and then boil it down some more in the big old cast iron kettle before using to make soap using rendered fat from butchering.

For fun you should read the description from the renaissance on how to make saltpeter for black powder from old dry-stored manure---it includes pouring rainwater through it until the taste changes...

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Wow, Thomas, that sounds pretty wild. Incidentally, some of the web page instructions advocate tasting the liquid wood ash extract to see if there is any bitter flavor. When I was a kid, I got hold of some analytical grade sodium hydroxide and found out that it was very aggressive at dissolving flesh. Much more so than acids like sulfuric and muriatic. The chemistry instructor said that even one part per million would break down the outer layers of one's skin. No way am I going to taste that stuff. I did try putting some on my fingertip to see if there was any reaction. I am very familiar with the slippery feeling of dissolving skin. No such reaction. So, although the pH is pretty high, there must be fairly low hydroxide ion concentration. I was intrigued about your description of hill country soapmaking. I suppose that the wood stove ash may be more alkaline, possibly due to the residence time mechanism. Also, potassium carbonate makes a poor, but operable, saponifier. So it may work somewhat. I have a lot of spare fat, so I may just carry out a trial reaction (without lime) to see what happens.

Thanks for the encouragement, Ice Czar. I will report on progress if there is any. Too many projects these days. I really like the idea of the wood gasifier. It is kind of sad to see a lot of those vapors go to waste during charcoal making. When making charcoal, I always try to have a pot of something cooking over the flames before dousing the wood, especially a dish like pot roast which takes a long time. Gotta to try to avoid waste.

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