From bigclivedotcom.
With the widespread ban on tungsten light bulbs, things that relied on their heat for operation has made them hard to find and expensive. Things like bulbs for lava lamps and glitter lamps.
Although there have been other USB powered glitter lamps, they often used things like magnetically coupled impellers to swirl the glitter around in a very violent manner that didn’t really give the proper effect. When I saw this unit in a shop window I realised that although it was clearly using LED illumination, the movement was definitely thermal convection. So I bought one for us to explore.
It is indeed thermal convection. It has two chunky resistors on the PCB creating the heat, and a measly single 5050 RGB LED for the light.
One of the most notable things about this light is that they have tuned the specific gravity of the liquid vial to perfection. The glitter has near neutral buoyancy at room temperature, with a tiny bias to the top over time when undisturbed. But even sunlight or holding the base creates enough thermal turbulence to get the glitter moving.
It’s easy to think that plastic is lightweight and easy to float, but in reality, the plastic you see floating in the sea or ponds is being held up by trapped air. The stuff you can’t see is at the bottom of the pool.
The plastic used for glitter is surprisingly heavy, and it takes a very high specific gravity to make it float. In some lamps they use a heavy solvent that has the advantage of giving a very fast flow, but also has the annoying trait of making the glitter stick to the side of the bottle.
In most glitter lamps the liquid is a mixture of water and a LOT of calcium nitrate, which has extremely high solubility. The downside of the calcium nitrate is that it corrodes exposed aluminium, so the glitter has to be coated to protect it from turning into clear plastic flakes. With very old glitter lamps the metallisation has often been eroded away.
When making your own calcium nitrate solution you have to get the purest stuff available, as any contaminants will show up as a haze and reduce the sparkle of the lamp. You can filter it though, and if you have lots of patience you can also make a batch and then let it settle for long enough that you can siphon the clear liquid from above the sediment layer.
Getting the perfect balance for the glitter is tricky. It requires a lot of trial and error, and for low heat sources the ratio is literally accurate to a few drips of water. With the high temperature lamps you have to balance it at the operating temperature, as thermal expansion of the liquid can change the density and cause the glitter to settle at the bottom when the bottle is hot.
It’s very difficult to tell if glitter is coated or not. Even trying to probe the surface with a meter is no guarantee of resilience, as some protective coatings will dissolve in liquid. I’ve found that holographic silver glitter has been pretty reliable, and also gives a great multi-colour scintillating effect.
I’m not sure if it’s possible to add some sort of corrosion inhibitor to the liquid. But even if you do find the metalization gets eaten off your glitter over time, it’s easy enough to decant the solution via a filter to remove the old glitter and try again with another type.
Although glitter lamps are very sparkly to look at, they also create a myriad of shapes and swirls of light around a dark room. They’re visually very pleasing things. I’ve had one running 24/7 for years with delicately balanced fluid and a 3W LED bulb to provide the heat and light.
If you can’t find high purity calcium nitrate then you can get useful results with "calcium and nitrogen" fertiliser bought from places like eBay. Although they can’t use the name in the listing due to nanny-culture they may show it in the images. A brand name is Calcinit. It may require a bit more time to filter and settle out the impurities. In some locations the use of distilled water may be required.
I guess that the manufacturers make large batches with highly accurate hydrometers and then just add the glitter and let it all stabilise during shipping and warehouse storage.
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