wood ash

A comprehensive set of analyses of wood ash composition from many tree species has been carried out by Emil Wolff,{{cite book|last1=Wolff|first1=Emil|title=Aschen-Analysen|url=https://archive.org/details/aschenanalysenv01wolfgoog|date=1871|publisher=Wiegandt und Hempel|location=Berlin}} among others. Several factors have a major impact on the composition:{{Citation |last=Siddique |first=Rafat |title=Wood Ash |date=2008 |url=http://link.springer.com/10.1007/978-3-540-74294-4_9 |work=Waste Materials and By-Products in Concrete |pages=303–321 |place=Berlin, Heidelberg |publisher=Springer Berlin Heidelberg |language=en |doi=10.1007/978-3-540-74294-4_9 |isbn=978-3-540-74293-7 |access-date=2022-07-24|url-access=subscription }}

1. Fine ash: Some studies include the solids escaping via the flue during combustion, while others do not.
2. Temperature of combustion.{{Cite journal|vauthors=Misra MK, Ragland KW, Baker AJ |year=1993|title=Wood Ash Composition as a Function of Furnace Temperature|url=http://www.fpl.fs.fed.us/documnts/pdf1993/misra93a.pdf|journal=Biomass and Bioenergy|volume=4|issue=2|pages=103–116|doi=10.1016/0961-9534(93)90032-Y}} Ash content yield decreases with increasing combustion temperature which produces two direct effects:
3. *Dissociation: Conversion of carbonates, sulfides, etc., to oxides results in no carbon, sulfur, carbonates, or sulfides. Some metallic oxides (e.g. mercuric oxide) even dissociate to their elemental state and/or vaporize completely at wood fire temperatures ({{Convert|600|C|F}}.)
4. *Volatilization: In studies in which the escaped ash is not measured, some combustion products may not be present at all. Arsenic for example is not volatile, but arsenic trioxide is (boiling point: {{convert|465|C}}).
5. Experimental process: If the ashes are exposed to the environment between combustion and the analysis, oxides may convert back to carbonates by reacting with carbon dioxide in the air. Hygroscopic substances meanwhile may absorb atmospheric moisture.
6. Type, age, and growing environment of the wood stock affect the composition of the wood (e.g. hardwood and softwood), and thus the ash. Hardwoods usually produce more ash than softwoods with bark and leaves producing more than internal parts of the trunk.

The burning of wood results in about 6–10% ashes on average. The residue ash of 0.43 and 1.82 percent of the original mass of burned wood (assuming dry basis, meaning that H₂O is driven off) is produced for certain woods if it is pyrolized until all volatiles disappear and it is burned at {{Convert|350|C|F}} for 8 hours.{{Efn|Woodchips of different wood species (Aspen, Yellow poplar, White oak, White oak bark, Douglas-fir bark) were pyrolyzed in a closed container in a furnace at {{convert|500|C|F}}.}} Also the conditions of the combustion affect the composition and amount of the residue ash, thus higher temperature will reduce the ash yield.{{Cite journal|vauthors=Etiegni L, Campbell AG |year=1991|title=Physical and chemical characteristics of wood ash|journal=Bioresource Technology|volume=37|issue=2|pages=173–178|doi=10.1016/0960-8524(91)90207-Z}}

Typically, wood ash contains the following major elements:{{cln|reason=What the ambiguous "%" stands for??? Is it a mass, volume or mole fraction??? Readers have no ability to read the writer's mind, and the writer must not assume that all readers are experts in this field! Using ambiguous units like "%" and "ppm" confuses and frustrates readers who are not experts in this field! Please clear this jargon!|date=May 2023}}{{Cite journal |last1=dos Santos |first1=Elvis Vieira |last2=Lima |first2=Michael Douglas Roque |last3=Dantas |first3=Kelly das Graças Fernandes |last4=Carvalho |first4=Fábio Israel Martins |last5=Gonçalves |first5=Delman de Almeida |last6=Silva |first6=Arystides Resende |last7=Sun |first7=Honggang |last8=Ferreira |first8=Marciel José |last9=Bufalino |first9=Lina |last10=Hein |first10=Paulo Ricardo Gherardi |last11=Protásio |first11=Thiago de Paula |date=2023-09-29 |title=The Inorganic Composition of Tachigali vulgaris Wood: Implications for Bioenergy and Nutrient Balances of Planted Forests in the Amazonia |url=https://doi.org/10.1007/s12155-023-10679-3 |journal=BioEnergy Research |volume=17 |pages=114–128 |language=en |doi=10.1007/s12155-023-10679-3 |s2cid=263292916 |issn=1939-1242|url-access=subscription }}

• Carbon (C) — 5–30%.
• Calcium (Ca) — 7–33%
• Potassium (K) — 3–10%
• Magnesium (Mg) — 1–2%
• Manganese (Mn) — 0.3–1.3%
• Phosphorus (P) — 0.3–1.4%
• Sodium (Na) — 0.2–0.5%.

As the wood burns, it produces different compounds depending on the temperature used. Some studies cite calcium carbonate ({{chem|CaCO₃}}) as the major constituent, others find no carbonate at all but calcium oxide ({{chem|CaO}}) instead. The latter is produced at higher temperatures (see calcination). The equilibrium reaction CaCO₃ → CO₂ + CaO has its equilibrium shifted leftward at {{convert|750|°C}} and high {{CO2}} partial pressure (such as in a wood fire) but shifted rightward at {{convert|900|°C}} or when {{CO2}} partial pressure is reduced.{{Citation |author1=Tarun R. Naik |title=Wood Ash: A New Source of Pozzolanic Material |year=2001 |publisher=Department of Civil Engineering and Mechanics, College of Engineering and Applied Science, The University of Wisconsin – Milwaukee |name-list-style=amp |author2=Rudolph N. Kraus |author3=Rakesh Kumar}}

Much of wood ash contains calcium carbonate (CaCO₃) as its major component, representing 25%{{Cite web |author=Lerner BR |date=16 November 2000 |title=Wood Ash in the Garden |url=https://www.purdue.edu/hla/sites/yardandgarden/wood-ash-in-the-garden/ |access-date=2023-10-21 |publisher=Purdue University, Department of Horticulture and Landscape Architecture}} or even 45% of total ash weight.{{Cite web |author=Hume E |date=11 April 2006 |title=Wood Ashes: How to use them in the Garden |url=http://www.humeseeds.com/ashes.htm |url-status=dead |archive-url=https://web.archive.org/web/20190705235959/http://www.humeseeds.com/ashes.htm |archive-date=2019-07-05 |publisher=Ed Hume Seeds}} At {{Convert|600|C|F}} CaCO₃ and K₂CO₃ were identified in one case.{{Efn|Woodchips of different wood species (Aspen, Yellow poplar, White oak, White oak bark, Douglas-fir bark) were pyrolyzed in a closed container in a furnace at {{convert|500|C|F}}.}} Less than 10% is potash, and less than 1% is phosphate.

There are trace elements of iron (Fe), manganese (Mn), zinc (Zn), copper (Cu) and some heavy metals. Their concentrations in ash vary due to combustion temperature. Decomposition of carbonates and the volatilization of potassium (K), sulfur (S), and trace amounts of copper (Cu) and boron (B) may result from increased temperature. The study has found that at raised temperature K, S, B, sodium (Na) and copper (Cu) decreased, whereas Mg, P, Mn, Al, Fe, and Si did not change relative to calcium (Ca). All of these trace elements are, however, present in the form of oxides at higher temperature of combustion. Some elements in wood ash (all fractions given in mass of elements per mass of ash) include:{{Rp|page=304}}

• Fe 1.6-55 ‰
• Si 6-170 ‰
• Al 1.2-45 ‰
• Mn 1-20 ‰
• As 0.6-50 ppm
• Cd 0.18-60 ppm
• Pb 2-500 ppm
• Cr 12-280 ppm
• Ni 10-140 ppm
• V 1.8-120 ppm

One study has determined that a slowly burning wood ({{Convert|100-200|C|F}} ) emissions typically include 16 alkenes, 5 alkadienes, 5 alkynes and several alkanes and arenes in proportions.{{Efn|By using gas chromatograpy analytical method.}}{{Cite journal |last1=Barrefors |first1=Gunnar |last2=Petersson |first2=Göran |date=April 1995 |title=Volatile hydrocarbons from domestic wood burning |url=https://linkinghub.elsevier.com/retrieve/pii/004565359500048D |journal=Chemosphere |language=en |volume=30 |issue=8 |pages=1551–1556 |doi=10.1016/0045-6535(95)00048-D|bibcode=1995Chmsp..30.1551B }} Ethene, acetylene and benzene were a major part at efficient combustion. Proportion of C₃-C₇ alkenes were found to be higher for smouldering. Benzene and 1,3-butadiene constituted ~10–20% and ~1–2% by mass of total non-methane hydrocarbons.

Wood ash can be used as a fertilizer used to enrich agricultural soil nutrition. In this role, wood ash serves as a source of potassium and calcium carbonate, the latter acting as a liming agent to neutralize acidic soils.

Wood ash can also be used as an amendment for organic hydroponic solutions, generally replacing inorganic compounds containing calcium, potassium, magnesium and phosphorus.{{cite book|last1=Sholto Douglas|first1=James|title=Advanced guide to hydroponics: (soiless cultivation)|date=1985|publisher=Pelham Books|location=London|isbn=9780720715712|pages=345–351|url=https://books.google.com/books?id=hykhAQAAMAAJ}}

Wood ash is commonly disposed of in landfills, but with rising disposal costs, ecologically friendly alternatives, such as serving as compost for agricultural and forestry applications, are becoming more popular.{{Cite journal|vauthors=Demeyer A, Voundi Nkana JC, Verloo MG |year=2001|title=Characteristics of wood ash and influence on soil properties and nutrient uptake: an overview|journal=Bioresource Technology|volume=77|issue=3|pages=287–95|doi=10.1016/S0960-8524(00)00043-2|pmid=11272014}} Because wood ash has a high char content, it can be used as an odor control agent, especially in composting operations.{{Cite journal|author1=Rosenfeld, P. |author2=Henry, C. |name-list-style=amp |year=2001|title=Activated Carbon and Wood Ash Sorption of Wastewater, Compost and Biosolids Odorants|journal=Water Environment Research|volume=7|issue=4|pages=388–393|doi=10.2175/106143001X139425 |s2cid=93782154 }}

Wood ash has a very long history of being used in ceramic glazes, particularly in the Chinese, Japanese and Korean traditions, though now used by many craft potters. It acts as a flux, reducing the melting point of the glaze.{{cite book|last1=Rogers|first1=Phil|title=Ash Glazes|date=2003|publisher=A&C Black|location=London|isbn=978-0-7136-57821|edition=2nd}}

=== Soaps ===

For thousands of years, plant or wood ash was leached with water, to yield an impure solution of potassium carbonate. This product could be mixed with oils or fats to produce a soft "soap" or soap like-product, as was done in ancient Sumeria, Europe, and Egypt.{{cite book |last1=McNeil |first1=Ian |title=An Encyclopedia of the History of Technology |date=2002 |publisher=Routledge |isbn=978-1-134-98165-6 |page=203 |url=https://books.google.com/books?id=o7yJAgAAQBAJ&pg=PA203 |language=en}} However only certain types of plants could produce a soap that actually lathered.{{cite book |last1=McNeil |first1=Ian |title=An Encyclopedia of the History of Technology |date=2002 |publisher=Routledge |isbn=978-1-134-98164-9 |page=214-215 |url=https://books.google.com/books?id=-sXFBQAAQBAJ&pg=PT214}} Later, medieval European soapmakers treated the wood ash solution with slaked lime, which contains calcium hydroxide, to get a hydroxide-rich solution for soapmaking.{{cite book |last1=Jungermann |first1=Eric |title=Glycerine: A Key Cosmetic Ingredient |date=2018 |publisher=Routledge |isbn=978-1-351-44458-3 |page=316 |url=https://books.google.com/books?id=qF1ZDwAAQBAJ&pg=PT316 |language=en}} However it was not until the invention of the Leblanc process that high quality sodium hydroxide could be mass produced, rendering obsolete the earlier forms of soap using crude wood or plant ash.{{cite book |first1=E |last1=Cook |title=American Journal of Pharmacy and the Sciences Supporting Public Health |date=1925 |publisher=Philadelphia College of Pharmacy and Science. |page=401 |url=https://books.google.com/books?id=iz4fAQAAIAAJ&pg=PA401 |language=en}} This was a revolutionary discovery that facilitated the modern soapmaking industry.{{sfn|Jungermann|2018|p=316}}

The ectomycorrhizal fungi Suillus granulatus and Paxillus involutus can release elements from wood ash.{{Cite journal|title=Metals, minerals and microbes: geomicrobiology and bioremediation|journal=Microbiology|author1-link=Geoffrey Michael Gadd|author=Geoffrey Michael Gadd|volume=156|issue = Pt 3|date=March 2010|pages=609–643|pmid = 20019082|doi=10.1099/mic.0.037143-0|doi-access=free}}

Wood ash is sometimes used in the process of nixtamalization, where certain types of corn (typically maize or sorghum)Odukoya, Julianah Olayemi; De Saeger, Sarah et al.: '[https://pmc.ncbi.nlm.nih.gov/articles/PMC7823315/ Effect of Selected Cooking Ingredients for Nixtamalization on the Reduction of Fusarium Mycotoxins in Maize and Sorghum]': National Center for Biotechnology InformationCabrera-Ramírez, A.H.; Luzardo-Ocampo I.; Ramírez-Jiménez, A.K.; Morales-Sánchez, E.; Campos-Vega, R.; Gaytán-Martínez, M.: '[https://www.sciencedirect.com/science/article/abs/pii/S0963996920302593 Effect of the nixtamalization process on the protein bioaccessibility of white and red sorghum flours during in vitro gastrointestinal digestion]': Food Research International

Volume 134, August 2020 are soaked and cooked in an alkali solution to improve nutritional content and decrease risk of mycotoxins. The alkali solution has historically been made from wood ash lye.

Nixtamalization was originally practiced in Mesoamerica, from which it spread northwards through various indigenous tribes of North America. In eastern North America, nixtamalized corn was traditionally eaten in porridges and stews, a dish that Europeans would call hominy.{{Cite web |last=Gomez-Misserian |first=Gabriela |date=2022-12-13 |title=Wood Ash Hominy: From Indigenous Nourishment to Southern Shame to Chef Secret |url=https://gardenandgun.com/articles/wood-ash-hominy-from-indigenous-nourishment-to-southern-shame-to-chef-secret/ |access-date=2024-03-25 |website=Garden & Gun |language=en-US}} Wood ash is also used as a preservative for some kinds of cheese, such as Morbier and Humboldt Fog.{{Cite web |date=2012-09-19 |title=Burn, baby, burn: Edible ash rounds out restaurant flavors |url=https://onmilwaukee.com/articles/edibleash |access-date=2024-03-25 |website=OnMilwaukee}}{{Cite web |last=Newman |first=Heather |date=2023-05-11 |title=Vegetables Burnt To Ash Are Unexpectedly A Culinary Masterpiece - The Daily Meal |url=https://www.thedailymeal.com/1283139/vegetables-burnt-ash-unexpectedly-culinary-masterpiece/ |access-date=2024-03-25 |website=Daily Meal |language=en-US}}

An early leavened bread was baked as early as 6000 BC by the Sumerians by placing the bread on heated stones and covering it with hot ash. The minerals in the wood ash could have supplemented the nutritional content of the dough as it was baked.Arzani A.: Emmer (Triticum turgidum spp. dicoccum) flour and breads. In Preedy V.R., Watson R.R., Patel V.B. (Eds. 2011), Flour and Breads and their Fortification in Health and Disease Prevention, Academic Press, California, pp. 69-78. In present day, the amount of wood ash content in bread flour, as measured by the Chopin alveograph,Li Vigni, M.: Monitoring Flour Performance in Bread Making. In Preedy V.R., Watson R.R., Patel V.B. (Eds. 2011), Flour and Breads and their Fortification in Health and Disease Prevention, Academic Press, California, pp. 69-78. is strictly regulated by France.{{cite journal |title=Décret n° 63-720 du 13 juillet 1963 relatif à la composition des farines de blé, de seigle et de méteil. |journal=Journal officiel de la République française. Lois et décrets n° 0169 du 20/07/1963 |date=20 July 1963 |volume=169 |page=6722 |url=https://www.legifrance.gouv.fr/jorf/id/JORFTEXT000000272197/}}

• Ash burner (traditional occupation)
• {{Annotated link|Ashery}}
• Bottom ash
• Charcoal
• Fly ash
• Joss paper
• Open burning of waste
• Wood glue
• Wood preservative
• Wood veneer

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