Sun Drying

Sun drying is the cheapest and easiest way to clean clam shells, but it has some limitations. Sun drying results in a fairly clean rather than perfectly clean product. Simply lay the clam shells out neatly, in a single layer—not in a pile—on the ground or pavement. Within a few weeks, the natural elements of sun and rain will have done a good but not excellent job of bleaching the shells. Some small bits of dried tissue or detritus may remain on the inside or outside of the shells.

Naturally bleached shells can sometimes be sold “as is” to tourists for use as garden ornaments or curios. A contingent of tourists out there wants shells with a “natural” appearance, which means that an imperfectly cleaned shell is desirable to them, but these folks are a small minority. Most buyers want their shells as close to perfectly clean as possible, particularly, and understandably, those who plan to use the shells as salad bowls or sashimi dishes. In that case, chemical cleaning with acids and bases is necessary to reveal the underlying beauty and value of the shells.

Chemical Bleaching

Really white shells can be obtained by using a chemical bleach called sodium hypochlorite, which is commonly sold in grocery stores as liquid laundry bleach; Clorox is a widely available brand. Sodium hypochlorite is an extremely strong chemical base, which attacks and dissolves the proteinaceous scum and tissue remnants on dead clam shells. Use it with caution as it is extremely caustic and can burn skin and eyes on contact.

Place the shells to be bleached inside a dry, 5-gallon bucket. Add approximately 2 gallons of fresh tap water (not seawater) to the bucket. Then add about one-half gallon of bleach, straight from the bottle (Figure 5). Add more bleach if you want to clean the shells clean faster and less if time is not critical. The shells will bleach fully in two to three days on average. After that, remove the shells, rinse them in fresh water, allow them to dry and store them in a clean, dry area to prevent mildewing. The diluted bleach solution may be used again but will gradually lose strength and require a fresh infusion of straight bleach.

Chemically bleached shells of Tridacna gigas, T. derasa, T. maxima and T. crocea require no further chemical cleaning, although some shellcraft applications call for mechanical modifications such as grinding or drilling, which will be discussed later.

Although sodium hypochlorite effectively whitens and removes proteinaceous materials from giant clam shells, it will not dissolve the scaly calcium carbonate deposits that are particularly evident on the colored shells of Hippopus hippopus, H. porcellanus or T. squamosa. For that, an acid dip is necessary.

Acid Dipping

The acid dip is a simple and quick procedure used to remove white encrusting materials from the shells of certain clam species in order to bring out the vibrancy and depth of the underlying shell colors. Acid cleaning is rarely, if ever, needed on clam species whose shells are all white naturally, such as T. derasa and T. gigas. Using acid on these species is, we feel, just a waste of time because bleach alone will get the shells perfectly white and marketable.

However, bleaching is only the first step of a two-step chemical cleaning process for the colorful giant clam shells, especially T. squamosa and H. hippopus. The second essential step is the acid dip.

A word of caution about the acid dipping process is in order before describing it. Because strong acids, like strong bases, can burn skin, eyes and lung tissues on contact, it is essential to wear suitable eye protection and gloves and to use these chemicals only in a very well ventilated area—preferably outdoors. Never work alone with these materials and always have immediate access to fresh running water in case of an accidental spill or splash. Discuss the potential hazards of these materials with your employees in advance of their use and outline a practical first aid strategy for dealing with chemical burns that could occur on the job-site.

Most hardware stores carry a product called muriatic acid, which is a 30 percent solution of hydrochloric acid (HCl). Muriatic acid is commonly used in the building trades for cleaning concrete or bricks.

First, fashion a simple dipping tool (Figure 6) by making a cradle of 14-gauge wire on the end of a small aquarium dip-net. A 2.5-gallon, lidded bucket is used for the acid dipping procedure. Begin by adding one gallon of clean, fresh water to the bucket. Then add one-half gallon of muriatic acid. Always add acid to water, never the reverse, to prevent dangerous splattering.

Next to the acid bucket, set a five-gallon bucket of flowing, fresh water. This will be used to rinse acid off the shell after the acid dip. The flowing fresh water is also a good safety precaution in case of an acid burn.

Place a dry, previously bleached shell into the dipping cradle and immerse it fully into the acid for no more than a few seconds (Figure 7 Figure 7). Then quickly remove it, and immerse it in the fresh water bucket (Figure 8). Place it in a plastic tray in a breezy area to drip dry (Figure 9). When fully dried, the shells are ready for sale “as is” or for crafting into other products. With a little practice, you'll be able to judge both the strength of the acid solution and the length of time required for the dipping.

Caution: If you are not very careful with this method, you can easily destroy a shell by leaving it in the acid dip too long. Be careful not to damage the lovely glossy surface of the concave inside of the shell; if the gloss is gone, you've overdone the acid dip. Under no circumstances should a shell be left indefinitely in the acid dip. It will get smaller and smaller and, eventually, disappear entirely.

After the acid dip and the fresh water rinse, lay the perfectly clean shells in a plastic tray to dry . When dry, they are ready for sale directly or for use in making any other type of shellcraft product.

A final note on chemical cleaning of giant clam shells. The acid dip is always the second step in the cleaning process. It should never be used if chemical bleaching has not been completed first. The reason is that acid dipping will not easily remove the proteinaceous material that sodium hypochlorite, used in step one, is so effective in stripping.