Whether you hunt rocks in the high desert of California, look for smoky quartz at Pikes Peak, Colorado, find rare gemstones in Arkansas or look for rocks on the trails of the Appalachian Mountains, your specimens need cleaning to find the real stone. The stones have an outer coating of clay and underneath the clay, a coating of iron or manganese oxide. Remove both the clay and iron to get to the beauty of the stone.
Lay the raw gemstones and smoky quartz outside in the shade and off the ground, so the clay can dry. Smoky quartz will fade if exposed to the heat of the sun.
Rinse the clay from stones with water from the garden hose. Repeat as many times as necessary. All the clay must be off the gemstones before you can go to the next step.
Use oxalic acid, which is available for purchase in the paint department of home improvement stores, to remove the iron oxide stain and keep the color of the smoky quartz and gemstones. Put on a long sleeve shirt, gloves, painter’s mask and eye protection glasses.
Put 3 qts. of water in a plastic container; add oxalic acid according to the directions on the box. Stir with large plastic spoon for five minutes until the acid dissolves.
Place gemstones and smoky quartz in the acid solution. Add enough water to cover the stones. Put lid on container and store in a high place away from children and pets for three days.
Remove rocks and wash under running water for three hours. Soak the rocks in clean water for 24 hours. Change the water every three hours. Remove rocks from the water and let dry.
For gemstones not very dirty, a stiff brush and some soapy water maybe all you need to get the rocks clean.
Do not use oxalic acid in the house. Use only outside in a well-vented area. Oxalic acid is a low grade acid and is the safest to use at home, but it is still an acid and care must be used around it.
Always wear safety equipment when working with acid.
Keep acid away from children and pets.
Vapors are poison.
Breathing fumes will damage lungs.