{"id":52468,"date":"2026-10-06T04:48:23","date_gmt":"2026-10-05T19:48:23","guid":{"rendered":"https:\/\/phys-edu.net\/wp\/?p=52468"},"modified":"2026-10-06T05:30:48","modified_gmt":"2026-10-05T20:30:48","slug":"i-built-a-volcano-and-it-was-explosively-fun-full-experiment-recipe-revealed-volcano-model-with-plaster-baking-soda","status":"publish","type":"post","link":"https:\/\/phys-edu.net\/wp\/?p=52468&lang=en","title":{"rendered":"We Built a Volcano\u2014and It Was Explosively Fun! The Ultimate Experiment Recipe Using Plaster and Baking Soda!"},"content":{"rendered":"

Hi, I’m Ken Kuwako, Science Trainer. Every day is an experiment.<\/strong><\/span><\/p>\n

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Let’s be honest: the best part of science class is actually “trying it out.”<\/span> Seeing students’ eyes light up and hearing a big “I get it!” makes us teachers just as happy. I taught a unit on volcanoes together with Mr. H, a student teacher at the time<\/strong>, and the eruption experiment we did turned out to be a real spark for curiosity.<\/span><\/p>\n

“How does the stickiness of magma affect the shape of a volcano?”<\/strong><\/p>\n

The fun of science isn’t just memorizing what’s in the textbook. It’s about seeing, touching, and feeling things for yourself. So we decided to build our own volcanic eruption models from everyday materials! This experiment looks simple at first glance, but it’s surprisingly deep.<\/p>\n

You only need four materials: plaster, baking soda, laundry starch glue, and water. Just by tweaking the mixing ratio of these four ingredients, the way the magma moves and how sticky it is changes completely. It feels like running a simulation of real volcanic activity.<\/p>\n

What I find especially fascinating is the chemical reaction that happens when you combine plaster (calcium sulfate: CaSO\u2084), baking soda (sodium bicarbonate: NaHCO\u2083), and water. It produces carbon dioxide (CO\u2082)!<\/p>\n

As the CO\u2082 forms, the mixture puffs up and swells, just like a real volcano slowly bulging before an eruption.<\/p>\n

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We tweaked the recipe again and again before we finally hit on one that made us say, “Oh, this might actually work!” It took a lot of time, honestly, but it reminded me that this is exactly what scientific inquiry is all about. And it didn’t stop there: the student teachers the following year, Mr. T and Mr. S, improved it even further.<\/strong> In this article, I’ll walk you through the ingredient ratios we arrived at after all that trial and error, and show you how a successful eruption looks!<\/p>\n

What You’ll Need<\/h2>\n

\u30fbPlastic container\u3000\u30fbPlaster 10 g \u00d7 2 \u2190 put in a zip-top storage bag\u3000\u30fbBaking soda 5 g \u00d7 2 \u2190 put in an evaporating dish\u3000\u30fbLaundry starch glue (PVA)\u3000\u30fbWater\u3000\u30fbSmall spoon (medicine spoon)\u3000\u30fbGlass stirring rod\u3000\u30fbTray\u3000\u30fbCorrugated plastic sheet<\/p>\n

For the plastic container, we used this one sold at Daiso. Size matters here, so if you want to follow the same method, please get the same one.<\/p>\n

Daiso 70 ml, pack of 4, round mini containers<\/a><\/p>\n

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Use a soldering iron to poke a hole in the bottom of the plastic container and in the corrugated plastic sheet, then cover the hole in the container with cloth tape ahead of time.<\/p>\n

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It’s a good idea to keep everything in a shallow tray.<\/p><\/div>\n

The size of the hole is the key. It should be about this big.<\/p>\n

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Now for the all-important recipe:<\/p>\n

Low-viscosity magma (runny type): 1 ml PVA laundry starch glue + 30 ml water
\nHigh-viscosity magma (sticky type): 10 ml PVA laundry starch glue + 15 ml water<\/p>\n

Prepare each mixture in advance in the containers above.<\/p>\n

\u3010Procedure\u3011<\/p>\n

\u2460 Stir the PVA glue and water in the plastic container well with the glass rod.<\/p>\n

\u2461 Add 10 g of plaster<\/strong> (from the zip-top bag) to the container of PVA glue and water.<\/p>\n

\u2462 Stir with the glass rod until the plaster, PVA glue, and water are thoroughly mixed.<\/p>\n

\u2463 Once it’s well mixed, add 5 g of baking soda<\/strong> and stir quickly so everything blends together<\/strong>.<\/p>\n

\u203b Don’t mix up the order of \u2462 and \u2463. Adding the baking soda in \u2463 is what triggers the chemical reaction that produces carbon dioxide. Also, if you leave the mixture at step \u2462 for 20 minutes or so, the plaster reacts with the water and hardens, and the experiment will fail. From what I found, plaster and water react and start to thicken and set in about 5 minutes.<\/strong><\/span><\/p>\n

\u203b In \u2463, it’s also important to mix everything quickly and put the lid on right away. Baking soda can sometimes clump together, so crush it finely with the small spoon beforehand.<\/strong><\/span><\/p>\n

\u2464 Close the lid, flip the container upside down onto the tray, and immediately peel off the tape.<\/p>\n

\u2465 Cover it with the corrugated plastic sheet that has the hole, and look down at the lava model from directly above to watch how the liquid (lava) spreads.<\/p>\n

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\u203b The experimenter must wear polyethylene gloves! Everyone should also wear a lab coat and safety goggles!<\/p>\n

Here’s how it actually turned out:<\/p>\n