{"id":17876,"date":"2026-04-19T16:15:55","date_gmt":"2026-04-19T10:45:55","guid":{"rendered":"https:\/\/aluminiummagazine.com\/mag\/?p=17876"},"modified":"2026-04-19T16:15:56","modified_gmt":"2026-04-19T10:45:56","slug":"potassium-alum-pickling-deodorant-guide","status":"publish","type":"post","link":"https:\/\/aluminiummagazine.com\/mag\/aluminium\/compounds\/potassium-alum-pickling-deodorant-guide.html","title":{"rendered":"Potassium Alum (KAl(SO\u2084)\u2082\u00b712H\u2082O): The Complete Guide"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\"><strong>Potassium alum<\/strong>, globally recognized simply as \u201c<strong>alum<\/strong>,\u201d is an ancient, highly useful double sulfate salt. Documented since antiquity for clarifying water and tanning leather, it remains a household staple. It forms large, clear octahedral crystals and is known for its sharp astringency. <strong>Today, it is used in natural crystal deodorants, pickling crisping agents, and styptic pencils for shaving.<\/strong><\/p>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">1. <strong>Basic Identification<\/strong><\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Chemical Formula:<\/strong> KAl(SO\u2084)\u2082\u00b712H\u2082O<\/li>\n\n\n\n<li><strong>Alternative Names:<\/strong> Potassium aluminum sulfate dodecahydrate, alum, tawas, kalinite<\/li>\n\n\n\n<li><strong>Molecular Weight:<\/strong> 474.39\u202fg\/mol<\/li>\n\n\n\n<li><strong>CAS Number:<\/strong> 7784-24-9<\/li>\n\n\n\n<li><strong>Appearance:<\/strong> Large, transparent or white translucent octahedral crystals or powder<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">2. <strong>Physical Properties<\/strong><\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th class=\"has-text-align-center\" data-align=\"center\">Property<\/th><th class=\"has-text-align-center\" data-align=\"center\">Potassium Alum (Dodecahydrate)<\/th><\/tr><\/thead><tbody><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Melting Point<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">92\u202f\u00b0C (198\u202f\u00b0F) \u2013 actually dissolves in its own water of crystallization<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Boiling Point<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">Loses water at 200\u202f\u00b0C; decomposes near 800\u202f\u00b0C<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Density<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">1.75\u202fg\/cm\u00b3<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Taste<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">Intensely astringent, sweetish, puckering<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Solubility<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">14\u202fg\/100\u202fmL cold water; 35.7\u202fg\/100\u202fmL hot water; insoluble in acetone and alcohol<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Potassium alum forms large, clear crystals that feel cool to the touch. In dry air, the surface may turn opaque white (efflorescence) as it slowly loses water.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">3. <strong>Chemical Behavior &amp; Reactions<\/strong><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">3.1 Mild Acidic Hydrolysis<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">In water, the aluminum ion hydrolyzes to produce a mildly acidic solution and a small amount of sticky aluminum hydroxide:<\/p><div class=\"pai-ad\" style=\"min-height:250px;visibility:hidden;\"><span style=\"display: block; text-align: center; font-size: 10px; margin: 0 0 10px 0; color: #999999;\">Ads<\/span>\r\n<!-- Display-300x250-1 -->\r\n<ins class=\"adsbygoogle\"\r\n     style=\"display:inline-block;width:300px;height:250px\"\r\n     data-ad-client=\"ca-pub-3838168351244230\"\r\n     data-ad-slot=\"9933646018\"><\/ins>\r\n<script>\r\n     (adsbygoogle = window.adsbygoogle || []).push({});\r\n<\/script><\/div>\n\n\n\n<p class=\"has-large-font-size wp-block-paragraph\"><strong>Al\u00b3\u207a + 3 H\u2082O \u21cc Al(OH)\u2083 + 3 H\u207a<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This sticky precipitate binds to suspended particles, enabling water clarification.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">3.2 Roasting \u2013 Making \u201cBurnt Alum\u201d<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Heating the crystals drives off water:<\/p><div class=\"pai-ad\" style=\"min-height:250px;visibility:hidden;\"><span style=\"display: block; text-align: center; font-size: 10px; margin: 0 0 10px 0; color: #999999;\">Ads<\/span>\r\n<!-- Display-300x250-1 -->\r\n<ins class=\"adsbygoogle\"\r\n     style=\"display:inline-block;width:300px;height:250px\"\r\n     data-ad-client=\"ca-pub-3838168351244230\"\r\n     data-ad-slot=\"9933646018\"><\/ins>\r\n<script>\r\n     (adsbygoogle = window.adsbygoogle || []).push({});\r\n<\/script><\/div>\n\n\n\n<p class=\"has-large-font-size wp-block-paragraph\"><strong>KAl(SO\u2084)\u2082\u00b712H\u2082O + Heat \u2192 KAl(SO\u2084)\u2082 + 12 H\u2082O \u2191<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">At 92\u202f\u00b0C, the crystals appear to melt as the structure collapses. Further heating to 200\u202f\u00b0C produces a porous white powder known as \u201cburnt alum.\u201d<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">4. <strong>Domestic &amp; Laboratory Applications<\/strong><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">4.1 Food Crisping (Pickling)<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Alum is added to pickling brines. The aluminum ions bind to pectin in cucumber cell walls, cross\u2011linking them and ensuring a crisp crunch rather than sogginess.<\/p><div class=\"pai-ad\" style=\"min-height:250px;visibility:hidden;\"><span style=\"display: block; text-align: center; font-size: 10px; margin: 0 0 10px 0; color: #999999;\">Ads<\/span>\r\n<!-- Display-300x250-1 -->\r\n<ins class=\"adsbygoogle\"\r\n     style=\"display:inline-block;width:300px;height:250px\"\r\n     data-ad-client=\"ca-pub-3838168351244230\"\r\n     data-ad-slot=\"9933646018\"><\/ins>\r\n<script>\r\n     (adsbygoogle = window.adsbygoogle || []).push({});\r\n<\/script><\/div>\n\n\n\n<h3 class=\"wp-block-heading\">4.2 Cosmetics \u2013 Crystal Deodorant &amp; Styptic Pencil<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Deodorant:<\/strong> A smooth block of potassium alum, when wet, transfers a thin salt layer to the skin. It does not block sweat but kills odor\u2011causing bacteria.<\/li>\n\n\n\n<li><strong>Styptic Pencil:<\/strong> Applied to shaving nicks, it constricts blood vessels and coagulates proteins, stopping bleeding almost instantly.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">4.3 Water Clarification<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">In rural areas, a chunk of alum added to muddy well\u2011water binds suspended dirt into a heavy sludge that settles, leaving clear water above.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">5. <strong>Safety &amp; Hazard Management<\/strong><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>General Safety:<\/strong> Potassium alum is FDA\u2011approved as a food additive (GRAS) and has an excellent safety profile.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th class=\"has-text-align-center\" data-align=\"center\">Route of Exposure<\/th><th>Effect<\/th><\/tr><\/thead><tbody><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Inhalation<\/strong><\/td><td>Powder may cause dry, stinging sensation in nose\/throat.<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Skin Contact<\/strong><\/td><td>Safe \u2013 intentionally used as deodorant. Dry powder may cause mild pulling\/dryness.<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Eye Contact<\/strong><\/td><td>Stinging and irritation, but generally not permanent corneal damage.<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Ingestion<\/strong><\/td><td>Safe in trace amounts (pickles). Eating straight powder causes throat puckering, nausea, vomiting due to irritation.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>PPE:<\/strong> None required for household use. Dust mask if grinding large amounts.<\/p><div class=\"pai-ad\" style=\"min-height:250px;visibility:hidden;\"><span style=\"display: block; text-align: center; font-size: 10px; margin: 0 0 10px 0; color: #999999;\">Ads<\/span>\r\n<!-- Display-300x250-1 -->\r\n<ins class=\"adsbygoogle\"\r\n     style=\"display:inline-block;width:300px;height:250px\"\r\n     data-ad-client=\"ca-pub-3838168351244230\"\r\n     data-ad-slot=\"9933646018\"><\/ins>\r\n<script>\r\n     (adsbygoogle = window.adsbygoogle || []).push({});\r\n<\/script><\/div>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>First Aid:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Eyes:<\/strong> Flush with water 10\u201115 minutes.<\/li>\n\n\n\n<li><strong>Ingestion:<\/strong> Drink water or milk to dilute; seek medical advice if large amount swallowed.<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">6. <strong>Storage &amp; Handling<\/strong><\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Container:<\/strong> Plastic or glass jar<\/li>\n\n\n\n<li><strong>Atmosphere:<\/strong> Normal air; high humidity may cause caking; extreme dry heat causes efflorescence<\/li>\n\n\n\n<li><strong>Location:<\/strong> Kitchen pantry, bathroom cabinet, or chemical shelf<\/li>\n\n\n\n<li><strong>Disposal:<\/strong> Can be thrown in trash or flushed down drain (safe for plumbing)<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">7. <strong>Environmental Impact<\/strong><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">In small amounts, potassium alum is environmentally benign. Large quantities dumped into a small pond would lower pH and harm aquatic life, so bulk disposal requires dilution.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">8. <strong>Comparison with Other Aluminium Compounds<\/strong><\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th class=\"has-text-align-center\" data-align=\"center\">Compound<\/th><th class=\"has-text-align-center\" data-align=\"center\">Formula<\/th><th>Primary Nature<\/th><th>Household Use<\/th><\/tr><\/thead><tbody><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Potassium Alum<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">KAl(SO\u2084)\u2082\u00b712H\u2082O<\/td><td>Safe, astringent double salt<\/td><td>Pickling, deodorant, styptic<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Aluminium Phosphide<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">AlP<\/td><td>Toxic gas releaser<\/td><td>None \u2013 lethal poison<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Aluminium Chloride<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">AlCl\u2083<\/td><td>Corrosive industrial acid<\/td><td>None \u2013 industrial use only<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">9. <strong>Frequently Asked Questions<\/strong><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Q: My \u201cnatural\u201d deodorant crystal says \u201cno harmful aluminum\u201d but lists potassium alum. Does it contain aluminum?<\/strong><br>A: Yes, it contains aluminum. However, potassium alum is a large, stable molecule that does not penetrate the skin as deeply as aluminum chlorohydrate. The marketing is misleading, but the compound is generally considered safe.<\/p><div class=\"pai-ad\" style=\"min-height:250px;visibility:hidden;\"><span style=\"display: block; text-align: center; font-size: 10px; margin: 0 0 10px 0; color: #999999;\">Ads<\/span>\r\n<!-- Display-300x250-1 -->\r\n<ins class=\"adsbygoogle\"\r\n     style=\"display:inline-block;width:300px;height:250px\"\r\n     data-ad-client=\"ca-pub-3838168351244230\"\r\n     data-ad-slot=\"9933646018\"><\/ins>\r\n<script>\r\n     (adsbygoogle = window.adsbygoogle || []).push({});\r\n<\/script><\/div>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Q: Why do my pickles still get soft even with alum?<\/strong><br>A: The blossom end of the cucumber contains enzymes that can break down cell walls. Always cut off the blossom end before pickling.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Q: If I add alum to muddy water, where does the mud go?<\/strong><br>A: The alum binds to the mud, forming a heavy sludge that sinks. You then pour or scoop the clear water from the top.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">10. <strong>Summary Data Sheet<\/strong><\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th class=\"has-text-align-center\" data-align=\"center\">Property<\/th><th class=\"has-text-align-center\" data-align=\"center\">Value<\/th><\/tr><\/thead><tbody><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Chemical Name<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">Potassium Aluminum Sulfate Dodecahydrate<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Common Name<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">Potash Alum \/ Pickling Alum<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Formula<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">KAl(SO\u2084)\u2082\u00b712H\u2082O<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Appearance<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">Large clear crystals or white powder<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Taste<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">Sour \/ astringent<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Defining Trait<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">Protein binder, tissue astringent<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Primary Utility<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">Styptic sticks, deodorant, pickling crispness<\/td><\/tr><\/tbody><\/table><\/figure>\n<\/p><div class=\"pai-ad\" style=\"min-height:250px;visibility:hidden;\"><span style=\"display: block; text-align: center; font-size: 10px; margin: 0 0 10px 0; color: #999999;\">Ads<\/span>\r\n<!-- Display-300x250-1 -->\r\n<ins class=\"adsbygoogle\"\r\n     style=\"display:inline-block;width:300px;height:250px\"\r\n     data-ad-client=\"ca-pub-3838168351244230\"\r\n     data-ad-slot=\"9933646018\"><\/ins>\r\n<script>\r\n     (adsbygoogle = window.adsbygoogle || []).push({});\r\n<\/script><\/div><script>document.addEventListener(\"DOMContentLoaded\",function(){\n        if(window.innerWidth <= 768){\n            if (\"immediate\" === \"delay\") {\n                setTimeout(function(){document.querySelectorAll(\".pai-ad\").forEach(el=>el.style.visibility=\"visible\")},0);\n            } else if (\"immediate\" === \"scroll\") {\n                window.addEventListener(\"scroll\",function(){\n                    let s=window.scrollY\/(document.body.scrollHeight-window.innerHeight);\n                    if(s>0.1){\n                        document.querySelectorAll(\".pai-ad\").forEach(el=>el.style.visibility=\"visible\");\n                    }\n                });\n            } else {\n                document.querySelectorAll(\".pai-ad\").forEach(el=>el.style.visibility=\"visible\");\n            }\n        } else {\n            document.querySelectorAll(\".pai-ad\").forEach(el=>el.remove());\n        }\n    });<\/script>","protected":false},"excerpt":{"rendered":"<p>Potassium alum, globally recognized simply as \u201calum,\u201d is an ancient, highly useful double sulfate salt. Documented since antiquity for clarifying water and tanning leather, it remains a household staple. It forms large, clear octahedral crystals and is known for its sharp astringency. Today, it is used in natural crystal deodorants, pickling crisping agents, and styptic &#8230; <a title=\"Potassium Alum (KAl(SO\u2084)\u2082\u00b712H\u2082O): The Complete Guide\" class=\"read-more\" href=\"https:\/\/aluminiummagazine.com\/mag\/aluminium\/compounds\/potassium-alum-pickling-deodorant-guide.html\" aria-label=\"Read more about Potassium Alum (KAl(SO\u2084)\u2082\u00b712H\u2082O): The Complete Guide\">Read more<\/a><\/p>\n","protected":false},"author":12,"featured_media":18010,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4155],"tags":[4141,4142],"class_list":["post-17876","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-compounds","tag-aluminium-compounds","tag-aluminum-formula"],"_links":{"self":[{"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/posts\/17876","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/users\/12"}],"replies":[{"embeddable":true,"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/comments?post=17876"}],"version-history":[{"count":0,"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/posts\/17876\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/media\/18010"}],"wp:attachment":[{"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/media?parent=17876"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/categories?post=17876"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/tags?post=17876"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}