Whether moldavites need cleaning to rid them of dust or of sand and clay residue after finding them, it is a good idea to follow one of the following procedures. They will help you to minimize the risk of damage while cleaning your stone.
Rinsing in water
Especially if your moldavites are on display, they will get dusty sooner or later. It is usually enough to rinse the stones with water and a little washing up liquid and rinse them under clean water and then let them dry.
In this we remove dust and it is very gentle to the stones. However, it does not remove the clay from the crevices.
Cleaning with a brush
Cleaning moldavites with a brush is the most effective method but there are some dangers. If the moldavite has protruding fine needles of lechatelierite they will be very likely broken off. If you are sure there are no lechatelierites on the stone, do use a brush. It is a safe way of cleaning for moldavites with severe abrasion and there are usually no lechatelierites on round stones without pronounced sculpture.
Use a soft brush, such as a soft toothbrush. Clean the stone under running water, which will wash away any residues. Those would scratch the surface. Brush the stone with circular strokes all over the surface, paying special attention to open bubbles and channels.
Ultrasonic cleaners are devices which use ultrasound to remove dirt from surface. The ultrasonic generator sets vibrating the tub with liquid, which, along with tiny bubbles, erodes dirt particles. The cleaner can remove dust, grease and clay residues even from cavities and creases.
An ideal liquid for an ultrasonic cleaner is demineralized (purified) water with detergent. I personally use cheaper solution.
Cheap solution for moldavite cleaning
I use tap water and a mixture of a little washing up liquid with washing powder. The results are very good, especially if warm water is used. If you do not have a cleaner with water-warming system, just use lukewarm tap water.
Minimizing of influence of cleaner on moldavites
As the bottom of the cleaner vibrates, you should place your moldavites into the plastic tub, which is a part of the cleaner. Thus you can minimize mechanical damage of the stones. Bigger stones with fine or sharp sculpture should not be put down on the bottom. You can either hold them or hang them on a piece of string or you can try putting them on a soft mat, e.g. polyethylene foam mat.
After cleaning the stones in the cleaner, rinse them under clean water.
Cleaning moldavites in an ultrasonic cleaner is perfect. Even the finest clay particles are removed from all creases of the sculpture.
Video – Cleaning of moldavites in ultrasonic cleaner
Particularly resistant dirt
On the surface of some moldavites there sometimes are very resistant forms of dirt. It can be ferruginous sandstone. As it is very appreciated among collectors, do NOT remove it!
In some moldavites (e.g. in those from the Brusna locality), the surface is covered with mineralized film. Such moldavite does not really look like a moldavite. Such film can only be removed by etching, which would, of course, damage the stone. Mechanical removal of the film is very laborious and time-consuming and the surface of the stone might get damaged as well. It is therefore better to leave the stone as it is and keep it as a rarity.
Cleaning raw moldavites from clay and sand
First, wash the moldavite under running water. Thus majority of sand and clay will be removed. After that, place the moldavites in an ultrasonic cleaner. Sometimes, even after ultrasonic cleaning, there is clay left in the creases of the sculpture. You can try cleaning it in the ultrasonic once more. If that does not work, disrupt the clay with a brush and then clean it again in the ultrasonic cleaner. There is a risk of breaking off the lechatelierite needles, though. Some clay residue can even be left on the stones on purpose. It is a sort of diversification. Finally, rinse the stone in clean water.