As observed, the oxidation process occurs relatively quickly, and visible iron oxides form within an hour. Shiny, small specks can also be seen, likely aluminum. The iron oxide sludge was surprisingly easy to filter out using a combination of a coarse filter, several coffee filters, and a wad of cotton.

A drop in temperature is a good sign, as nitrate salts tend to absorb energy when dissolving in water. This property is utilized in certain technical and medical applications for cooling purposes.

Next, I poured the nearly clear liquid into a shallow dish with as much surface area exposed to air as possible, ensuring at least a 3mm depth of liquid. This helps facilitate the formation of larger crystals. Now, we need time and warmth to allow the liquid to evaporate slowly, oversaturating the solution and causing crystallization. Salts tend to adhere to already existing crystal structures, which initially form on a microscopic level. These structures can also be impurities, often referred to as “seed crystals” in the field. Ideally, salts prefer to adhere symmetrically to similar salts.

After just one day (with 3/4 of the liquid already evaporated), many small crystals can already be seen in the solution. I briefly rinsed them with ice-cold water and immediately placed them back in a warm environment to remove any fine impurities. The result is many small barium crystals.

It’s clear that multiple recrystallization cycles, possibly with an additional filtration step, would be needed to remove all impurities. However, the results are already quite impressive.

How do we know it’s barium nitrate? Well, salts have distinct crystal structures depending on their composition. These structures influence crystal growth and, when the crystals become large enough, can be observed on a macroscopic scale, as seen here. Almost every salt has its unique crystal structure, making it possible to estimate its composition based on this characteristic. The purer the crystal, the more pronounced its structure becomes.

I have another source of a nitrate mixture. As the holder of a license to obtain this substance, I will not go into further detail about what it is or how one might (potentially illegally) acquire it. This is meant to focus solely on the fascination of crystal formation.

The approach is the same. First, I dissolved the substance in water, let it sit, and then filtered it.

This is crystallizing potassium nitrate, which forms beautifully clean needle-like crystals. The slight cloudiness is an indication of water-soluble impurities.

This particular crystal turned out to be a particularly beautiful and clean needle. I obtained several larger ones, although they all grew somewhat asymmetrically and irregularly. The largest measured approximately 8 cm.