Off-Grid Refrigeration Using Fire And Salt

October 18, 2026 by Bryan Cockfield 31 Comments

Refrigeration has been a challenge for humanity since the start. Ancient civilizations in dry climates like Persia and Egypt could use evaporative cooling on a large scale with specialized architecture, and with easy access to electricity modern civilization can cool down almost anything it wants. But whether in a refrigerator or heat pump, the electricity demands can get out of hand quickly, and heat-driven systems often require dangerous or hard-to-get chemicals. But [Greenhill Forge] has crafted a system that creates effective refrigeration with only fire and salt… and a bit of electricity.

Heat-driven systems are called absorption coolers. In this design, water is used as a refrigerant and forced to a very low pressure so that it can boil at a low temperature. When it boils it absorbs heat from the surrounding environment, and then that water vapor can be moved and condensed where it gives off that heat. The build has a few distinct loops to make all of this happen. The generator loop holds the heat source and a tank of water mixed with road salt. Boiled water travels up a tube to a condenser. A valve here is opened slightly to allow the water to drip into the absorber section, where it is under low pressure and boils rapidly. The vapor is carried away by the third system, which uses a shower of the salt solution to quickly suck up the vapor and move it away from the cooled area.

There is a small amount of electricity needed to run pumps and fans, but to keep this off-grid this requirement is easily met by a small solar panel or battery. The bulk of the energy is from the fire which boils the saltwater solution. [Greenhill Forge] added a number of temperature and pressure sensors to monitor and control the system as well, and in his firsts tests the refrigeration system was able to get to about 5° C with an ambient temperature around 16° C. That’s not quite the temperature needed for a refrigerator, but not bad for only salt and fire. [Greenhill Forge] has a number of other ingenious off-grid builds like this sawdust stove and a magnetic induction water heater.

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Low Current Density Nickel Plating

October 8, 2026 by Al Williams 19 Comments

We imagine that electroplating is like making PC boards or soldering surface-mount chips. Before you’ve done it, it seems like a lot. Afterward, you can’t remember why it was such a big deal. [Kovancapol] wants to show you how to plate a mirror-finish nickel over your tools, and while it looks like a lot to set up, we are guessing that it gets easy once you have everything together.

There is a bit of chemical setup, as you might expect with reagents like nickel sulfate and nickel chloride. Then there’s the glassware, nickel anodes, and a power supply. As you can see in the video, the results look very nice. We can’t help but wonder what other uses you might have for this process.

A conductive coating on a 3D print might be feasible. We aren’t sure soldering PCB traces would be worth it since nickel gets hard to solder as it oxidizes. You can mix and match plating for some pretty impressive results.

How To Grow A Giant Crystal From Copper Sulfate

October 5, 2026 by Maya Posch 17 Comments

Copper sulfate crystals are probably among one of the prettiest crystals you can grow at home, with even just a simple setup with some copper scrap and vinegar already capable of producing lots of them. Yet what if you want to grow really big ones? In that case the [Crystalverse] has got your back, with a recent video that expands on an older blog post.

In lieu of the copper-and-vinegar approach you can also obtain copper sulfate directly, since it’s a common fungicide, rootkiller as well as drying agent. This means that your local brick-and-mortar retailer or favorite online store probably has a few kg of the stuff available for sale.

As with most large crystal growing procedures the key is to have a saturated solution, which for copper sulfate just takes near-boiling water, to create a mesmerizingly blue liquid if there are no contaminants in it. By adding slightly more copper sulfate there are also crystallization sites on the bottom of the jar to draw these away from your large crystal.

From there it’s the same as with growing other large crystals – even those from sugar – with a seed crystal suspended into the solution, along with a silent prayer to the crystal gods that said seed crystal continues to grow without any defects. One gotcha with copper sulfate crystals is that the intense blue color is largely due to the presence of water molecules. This means that once it dehydrates, it turns effectively white.

Also of note that is the slower the crystal grows, the better the result is likely to be. During the months that it takes for these large crystals to grow, you need to carefully manage the copper sulfate solution, remove competing crystals on the bottom of the container and keep the temperature as constant as possible.

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Basically, Galvanizing Metal Without Acid

September 26, 2026 by Bryan Cockfield 31 Comments

As useful as steel and iron are to the modern world, their tendency to rust is a major downside. There’s a spectrum of ways to prevent it, from quickly slapping on a coat of paint to alloying, chromizing, or physical vapor deposition. For a middle ground accessible to the home shop, galvanizing is a go-to method of rust prevention that deposits a layer of zinc onto the metal instead, but even this generally involves the use of strong acids. This method makes galvanizing accessible without any acids. (Spoiler alert: substitute strong bases.)

Although the acids are omitted, the solution is caustic, so similar safety measures are still advised. The first step in the process is to dissolve sodium hydroxide into a container of distilled water. Metallic zinc can then be dissolved in the solution, with a bit of sugar and liquid soap to improve the finished quality of the coating. An electric current is applied to the solution, using a graphite plate at the anode and the part to be electroplated as the cathode. After some time, the part will be uniformly coated in a layer of zinc, which can then be brightened in a solution of only-mildly-acidic citric acid if needed.

One of the benefits of using a strong base to galvanize a metal part, beyond the preference of avoiding strong acids, is that this process can be better at plating parts that are non-uniform in shape, so things with deep crevices or other odd shapes that might coat unevenly in acid. If there’s a preference for electroplating with acid, there are some ways of producing one’s own using various methods.

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Making Better Rubies At Home

August 24, 2026 by Maya Posch 15 Comments

Not the prettiest ruby, for sure. (Credit: Gems of Science, YouTube)

Sapphires and rubies aren’t just pretty, they also got a range of practical uses. This makes it even more useful to be able to make them at home for obviously completely innocent experiments. Cue [Gems of Science] and his attempts to make good-looking rubies, without resorting to the brute-force laser blasting approach that [Styropyro] previously used to create murky-looking gems.

That basic method used involves blasting aluminium oxide with a laser, which results in a container full of what are technically gems, but – as the image on the right makes clear – not exactly the prettiest or easiest to shine up. Much of the problem here is that these are hollow geodes composed of countless tiny crystals instead of solid singular crystals.

Although there are commercial ways to fairly easily create large crystals from a small seed crystal, none of these lend themselves to a DIY hobbyist with just a garage to muck about in. This leaves one alternative: the flux method. Rather than melting the material that will be grown onto the seed crystal, this flux crystal growth method uses a solvent (flux) and temperatures that a home kiln can achieve.

These rubies may be small, but are very shiny. (Credit: Gems of Science, YouTube)

Of note here is also that it’s the addition of Cr³⁺ ions into the base Al₂O₃ matrix that makes a ruby into a ruby, by giving it its red glow. In order to grow crystals this way you need to pick not only a suitable solvent, but also use a crucible that doesn’t want to become part of said crystal. Unfortunately a platinum crucible runs into the thousands of USD, but a graphite crucible should do if you keep oxygen away from it.

For the flux molybdenum oxide was used, mixed with chromium oxide and aluminium oxide to provide the ingredients for crystal growth. Unfortunately added charcoal interfered with the molybdenum, ruining that batch. This led to trying out more crucible types to find a recipe that worked, thereby finding out that an ‘alumina’ crucible also contained silica, which poisons the reaction, resulting in only tiny ruby crystals.

Ultimately pure alumina crucibles seemed to work great, until they began to shatter en masse, resulting in pained wallet noises and the purchases of some pre-loved platinum crucibles. This worked really well, but now the flux was evaporating too quickly to enable large crystal growth, thus requiring additives to stabilize it. Along with temperature cycling to induce the growth of larger crystals, this finally generated some solid results. After a first batch of smaller rubies, next up larger ones of up to 10 mm were grown.

While cutting one of these large rubies to set into a ring it was clear that it was still rather flawed, with pockets of flux captured into the crystal, but with the basic method now more or less dialed in it should be possible to address these small flaws as well.

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Turning Energy Drinks Into Rocket Fuel

August 15, 2026 by Maya Posch 13 Comments

Sometimes claimed to give you wings, energy drinks can, at the very least, be used to make rockets fly. This is what [Nate Scovill] did in a recent video, where cans of the sugary stuff are processed to give a rocket its proverbial wings.

The basic concept is so-called rocket candy, which uses the fact that sugar is a pretty decent fuel type that — when combined with an oxidizer like potassium nitrate — can be turned into solid rocket fuel. Naturally it’d be easiest to start off with a pure source of sucrose or sorbitol for the sugar, but what if you only have access to cans of sugary soda?

Removing the moisture from the energy drink was the obvious first step, as water and rocket fuel aren’t a great mix. Adding and mixing potassium nitrate to the resulting thick syrup created the fuel-oxidizer mixture, also known as rocket fuel. This did take a detour involving removing the carbonation using a vacuum chamber, as CO₂ and fire do not really like each other either.

We previously covered making your own rocket candy, though it’s far from the only rocket fuel that can be made at home using products bought at the local supermarket. Obviously, doing so comes with a whole heap of risks, not least of which is the notion that the difference between a rocket and a bomb is a pretty thin and fuzzy line that you do not want to accidentally cross.

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Polystyrene Foam Can Be Gasoline With Some Help

August 4, 2026 by Maya Posch 25 Comments

Styrofoam – or closed-cell extruded polystyrene (XPS) foam if you want to be precise – is one of those materials that is both super versatile for packaging and insulation, but also a menace when it comes to disposal, even if you ignore that the monomer styrene (C₈H₈) is a known mutagenic toxin. One of the more creative ways to deal with the metric tons of polystyrene waste generated each year is to turn it into gasoline, as demonstrated by [Lowered Expectations] in a recent video.

With polystyrene being just another hydrocarbon polymer, the idea of turning these polymers into the mixture of hydrocarbon chains we call ‘gasoline’ isn’t so crazy. The problem is mostly doing it in a way that makes some economic sense and doesn’t risk turning your domicile into a hazmat risk site or threaten the health of you, your loved ones and the neighborhood.

The method demonstrated in the video uses fairly basic methods involving pyrolysis and distillation. The first step involves dissolving the polystyrene in gasoline that was previously recovered from stale gasoline, which is another dangerously fun science experiment. This creates a thick slurry that’s then put into the distillation flask for the heating phase.

After testing the distillates for spark ignition the useful distillates were combined with fuel stabilizer added. Before tossing this into a gasoline engine tank for further testing, the concerns of auto-polymerization of styrene monomers are addressed, which requires special inhibiters.

Although this mixture runs a gasoline generator just fine, a borescope inspection of the cylinders showed a build-up of a shiny, gummy residue. There’s also the issue that this mixture contains styrene monomers, which are as noted very unhealthy to breathe in from either the fuel or any remaining monomers in the exhaust. Definitely not something to try at home, basically.

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