an excerpt from "Collecting Crystals" by Mike and Darcy Howard
||How to start
06.21.00--Now that you have collected some nice quartz specimens, and because they are still dirty, you need to know how to clean them. If you have just a few pieces, use an old toothbrush to get the clay off. Otherwise, start by building a 2 by 2 foot framed 0.25 inch mesh screen. You can get this type of screen, called hardware cloth, at your local hardware or farm and garden store. Remove the newspaper wrapping and let the specimens dry on the screen for a couple of days. Keep everything in the shade to prevent the crystal from heating up too rapidly in direct sunlight. When the clay is well cracked and dried, rinse with a garden hose. Let dry a couple of days and repeat the cycle.
Removing the iron
Then you are ready for the next step. If the crystal only has a very light iron staining, then a few days soaking in a weak oxalic acid solution in a covered plastic bucket will remove it. If the iron staining is heavy, then we must cook the quartz in an acid solution. People have many ways to clean quartz, all involving basically the same scenario. Your specimens may be coated by iron or manganese oxides, with or without clay and you wish to remove the staining so the specimens are as clean as possible.
Use with care
The most commonly used, readily accessible chemical for cleaning quartz is oxalic acid, which may be bought as a white crystalline powder. It may be purchased from many mineral dealers in Arkansas, especially those who specialize in quartz. When mixed with water at a measure of a few ounces per gallon and then heated to just below a boil, oxalic acid is capable of removing all but the most stubborn iron staining. It is a weak organic acid, but don't kid yourself, it will hurt you especially if you breath the fumes. So use it only outside in a protected and well vented area, preferably where no children may gain access.
Some key points
There are several key points to preparing quartz to be cleaned. First, you need to remove the clay. This is accomplished by cycling the specimens through the several wet and dry periods to loosen and wash the clay away. You may have to use a pressure washer to remove the last of the clay. Remember: this first step is critical.
You do not want to have to clean the material several times, and that is exactly what you will have to do if the clay is not completely removed before the first acid cleaning. Trim your specimens to the size and shape you want before cleaning in acid. Remove the dinged or broken portions. This action will save the time of re-cleaning after trimming and the cost of the additional acid used to clean what you trimmed off and threw away.
Once you have the specimens prepared for acid treatment, then you must consider the situation. Do you have small specimens and just a gallon or two of crystals or do you have some big pieces? Maybe you got lucky and have one piece that would fill a 5-gallon plastic bucket!
Tips for using oxalic acid
Don't use expensive reagent or chemical grade oxalic from the pharmacy. Instead, when you visit Arkansas, ask at the crystal shops around Mount Ida or Jessieville. Many dealers provide written instructions and sell it by the pound or multi-pound package for around $3 per pound or $2.50 per pound for 5 pounds. How much do you need to buy? It depends. Did you get a 5 gallon bucket of quartz specimens or a 3/4 ton truck bed full? A five gallon bucket might take 1 to 1.5 pounds of acid to 5 gallons of water if the crystal is really dirty.
Start with a weaker solution first and build its strength if you need to. Also, the acid solution will not be used up until it turns dark emerald green by becoming saturated with the removed iron, so you can reuse it by adding a very small amount of fresh water and powdered acid to the old solution. Remember: it is an acid, though a relatively weak one. Do not leave this stuff where kids or animals might get into it. I usually wear dish washing gloves when working around it even though it will not burn skin, it will let you know if you have a scratch or cut, by burning you. Take care not to get any acid in your eyes. I always keep a garden hose handy so when I get a splash, I can rinse it off immediately. Accidents happen!
Experiences with Cookers
To clean small pieces, you need to search for cookers at yard/garage sales. Whenever you find a crock pot (the slow cooker ceramic-lined type) for $4 or less, buy it!.You can get some 10 to 12 processing cycles before the acid finds its way through a hairline crack in the ceramic inner glaze and corrodes the heating element. But that's OK, if you got 10 gallons of small quartz specimens cleaned, then it's worth it.
Place the specimens in the crock pot, add cold water, then a couple of ounces of dry oxalic acid and top off with cool water. Be sure the water is above the crystals because any crystal sticking out will not get cleaned. Cover with the glass or plastic lid, plug in and set the temperature control to low. Check this every two days and add a little warm water as needed to keep the crystals submerged. DO NOT DO THIS IN THE HOUSE. ACID VAPORS ARE POISONOUS.
After about a week, turn the crock pot off and let it cool down overnight. Do not get too anxious to pull the crystals out while they are hot or they will shatter from the thermal shock. Then remove the specimens and rinse them thoroughly. If your specimens begins to grow a white powder as they dry, place them back in a clean crock pot, add water and a 1/3 a cup of baking soda, and cook overnight. This will neutralize the remaining acid as it comes out of the nooks and crannies of the specimens. If this does not work to get rid of the white powder problem, then you will need to cook them again in clean water with baking soda as a neutralizer.
Disposing of acid
To dispose of a volume of spent oxalic acid (it will be a dark emerald green color from the dissolved iron it contains), add lime (CaO) like you use in the garden to the liquid until you get no reaction. Then it will be neutralized due to the formation of harmless calcium oxalate. You can just dump it on the ground like I do where I wash my crystals with a garden hose. That way, the next time I wash rocks or it rains the material is diluted. If you lived in town or in an apartment, just take a funnel, pour it in a 1-gallon milk jug and put it in the trash or in a dumpster. Since its neutralized, it is not considered a hazardous material and since it is water-based it is not flammable.
This information is an excerpt from Collecting Crystals: A Guide to Quartz in Arkansas by Darcy and Mike Howard, ©2000