I have etched many many iron meteorites over the last 8 years. It seems that very often I get emails regarding the subject. I am by no means saying my way is the best or only way to etch. This is not intended as a guide or "how to" instead I'm simply saying this is the way I do it. (Do not try this at home)
Secrets to Cutting, Etching, and Preserving Iron meteorites
Etching as it relates to iron meteorites is simply the process of revealing its hidden crystalline structure. This structure is called a widmanstatten pattern. This pattern is unique to meteorites and no two meteorites display the same exact pattern. Each pattern is made up of crystals that look like plates which range in size from very fine to very coarse.
Some of the finest patterns are seen in plessitic irons such as the Taza iron meteorite. Taza displays an etched pattern that somewhat resembles snow flakes or stars. Other Iron meteorites such as Sikote Alin have very large plates, some are an inch or more across. Some of the most beautiful structures are widmanstatten patterns with fine to medium size plates. These would include Gibeon, Cape York, Henbury or Toluca.
Canyon Diablo, Nantan and Odessa are examples of iron meteorites that not only display a beautiful widmanstatten pattern but often have gorgeous inclusions. A simple graphite inclusion on the exterior of one of these meteorites goes almost unnoticed. However, when properly sliced and prepared a large black graphite inclusion in the center of an etch is truly beautiful.
Choosing an iron meteorite to etch is not quite as easy as it may sound. Iron meteorites can be as different and unique as the patterns themselves. Ataxite meteorites such as chinga are made up almost entirely of taenite and do not etch. A hexahedrite meteorite made up mostly of kamacite will etch but only very fine lines will appear. These are called neumann lines, and though technically it is an etch, it’s not much to look at.
The problem in choosing an iron meteorite to etch is all meteorites are not equal. Even meteorites from the very same fall don’t always display the same quality etch. For example while most Gibeon meteorites etch wonderfully it is not too uncommon to find one that displays a blurry or muddy pattern. On occasion one may even run across a Gibeon with no discernable etch whatsoever.
It is important to always window any iron meteorite before cutting and etching. This window will allow one to etch only that small area and test its etch. If the pattern displayed is brilliant and beautiful then the specimen is ready for cutting. But if the etch is dull or even non existent its time to find another specimen to cut.
Iron meteorites also differ in hardness and therefore some cut much quicker and easier than others. The most difficult to slice are those with inclusions. The large inclusions in a Canyon Diablo, Nantan or Odessa meteorite make them very hard to cut. This is partly because of the mineral schreibersite which is very hard not to mention the presence of microscopic diamonds that sometimes surround their inclusions.
The Gibeon meteorite with its fine widmanstatten pattern is probably one of the best meteorites to etch. Along with the fact that it is relatively inclusion free and cuts very easily, it is also very stable and when properly prepared will remain stable for years. It also has one of the most beautiful and recognizable etches of any meteorite. No surprise it is the meteorite of choice for expensive meteorite watches, jewelry and knives.
Once an iron meteorite has been chosen to slice and etch the question becomes how does one cut what is by any standard a very hard rock? There are many methods for cutting these extra terrestrial irons. Two common methods include expensive circular diamond blades on a circular saw or a large band saw. One thing is for sure, neither one is cheap nor practical. This may be the reason there is not more etching done by the average Joe meteorite collector.
While most circular diamond blades and band saws will cut an iron meteorite both have their drawbacks. The circular diamond blade is very expensive, it can cost from $75 to $150 for a single blade. The other problem is that a circular diamond blade is very slow going and can take up to 6 to 8 hours for a single cut. However, if one is patient it will give a straight cut.
If speed is a concern a band saw seems to be a little better choice. Fitted with a good bi-metal blade a band saw can cut an iron meteorite much quicker than a circular diamond blade. A bi-metal blade is also much cheaper, it costs about $35 to $55 depending on the length of the particular blade. Diamond blades for a band saw can also be used but they are very expensive around $200 each.
The biggest problem one may have with a band saw is unless it is very large and has a blade width of 1 inch or more it will probably tend to wander. This wandering will leave slices uneven, they tend to be either concave or convex. Neither are conducive to a really great etch. Also the larger the blade width the more a band saw blade will gouge into the side of the slice being cut. This leaves horizontal lines that must be sanded out before etching, thus adding hours of work in preparation time.
The best overall method for slicing a smaller 1 to 5 kilo iron is neither of the above. An abrasive type blade on a water cooled drop saw seems to work best. This abrasive blade made by SPEDECUT (602 276 0077) part # S-5560 is very thin. Its dimensions are 12” x 1/16” with either 7/8” or 1” arbor.
The advantages of this blade are many. First of all it is thin, very thin, at 1/16” thick it is even thinner than a dime, so there is very little loss. In most instances around 15% loss as opposed to 25% to 30% with the other methods. Second it is cheap, it costs under $5 per blade. It is an abrasive blade which means that the cut is so clean and smooth that there are no hours spent sanding off the deep marks a band saw blade leaves behind.
Most importantly it works, it is usually faster and cuts straighter than either a circular diamond blade or a band saw. In most cases it will take only minutes not hours to make a single slice. One blade lasts surprisingly long, cut for cut it may last as long as a band saw blade and in some instances will even outlast a circular diamond blade.
Keep in mind that because the abrasive blade is only about the size of an old vinyl LP it will only work on 1 to 5 kilo iron meteorites. Larger meteorites may first need to be halved or quartered on a large band saw to make them small enough to fit in the drop saw vice. Of course this depends on the shape of the particular meteorite. If it is shaped like a small loaf of bread it may weigh much more and still fit fine.
When slicing a meteorite to etch it should be noted that full slices about 3/16” thick seem to be the most popular. The height and width of the slice of course depend on the height and width of the particular meteorite being cut. A nicely etched end piece is also a wonderful addition to any collection, and since only one face is etched on an end piece it is also much less difficult to prepare.
Once the slices have been made, the next step is to prepare them for etching. This is accomplished by sanding the slices smooth, and can be done with any type of sander, even a simple hand held sander that can be purchased for around $30 will do. Begin by sanding with 60 grit, then 120, 220, 400 and finally ending with 600 grit. Each grit will progressively make finer and finer scratches, continue until the scratches are so fine that by the time 600 grit is reached the piece will begin to look semi-polished. If done properly this should be more than enough to insure all the saw marks have been removed, and that when etched, the widmanstatten pattern will stand out. If the slice still shows saw marks simply repeat the sanding process until they have all been removed.
Some meteorites because of their fine widmanstatten pattern such as Gibeon or Muonionalusta are far more forgiving when it comes to sanding. In fact some Gibeon meteorites can be etched without any sanding whatsoever and still show a beautiful pattern. However, other meteorites with larger structures like Sikhote alin tend to magnify saw marks that have not been removed. In general the better a meteorite has been prepared during the sanding phase the better the etch will be.
There are several ways to chemically etch an iron meteorite. Two popular methods used in etching iron meteorites include the use of Ferric chloride, and Nitol. Nitol which is an alcohol/ nitric acid mixture is what most believe works best. This is because nitol seems to leave the etched slice more stable than ferric chloride. There is however a place for ferric chloride in etching irons. It can be used, but only in small amounts as ferric chloride tends to promote rusting.
Etching an iron meteorite seems to be about 50% science and 50% art. The science is easy, just a few steps followed in the right sequence and there it is. The art is different and is much more difficult to define let alone teach. Poorly etched slices make one wonder why a person would do that to a perfectly good meteorite, and slices with muddy or dim etches are better left uncut. On the other hand wonderfully prepared slices with superb holographic type etches are beautiful. Even better to some are the beautifully etched spheres, eggs and pyramids, not to mention etched knives, watch faces and, jewelry.
The nitric acid used in nitol for etching iron meteorites can be purchased at most any chemical supply store for about $10 per 6 ounce bottle. A bottle of this size will etch many slices, as it only takes a few drops of acid to etch each slice. Keep in mind that since September 11, 2001 the use of chemicals like nitric acid will need to be documented and signed for. Nitric acid is very dangerous and should be handled with care. Always use rubber gloves, an apron, and proper eye protection when handling the acid.
The nitric acid and alcohol mixture called nitol can range from between 5% to 12% nitric acid. It is usually better to start somewhere around 5% and experiment with a little more nitric acid if the etch is weak or is coming along too slowly. Too much nitric acid in the mix can “burn” the etch and leave it very dull. If this happens the slice will need to be re-sanded and then re-etched using less nitric acid.
One can use expensive chemical grade alcohol or even Ever clear when making nitol. If desired this more expensive alcohol can be purchased at the same chemical supply store as the nitric acid. Ever clear is alcohol meant for consumption in mixed drinks and can be bought at your local drug or liquor store. While both types of alcohol will do the job just fine they are both very expensive and very unnecessary.
Rubbing alcohol that is at least 70% alcohol works wonderfully and is much cheaper. At a cost of about $1 per pint one can etch quite a few slices without going broke. Don’t worry about the 30% water in the rubbing alcohol. Since the meteorite will have to be washed vigorously in soap and water after the etch, a little water before will not affect the beauty of the etch or the stability of the meteorite.
When making nitol one very important rule to remember is to never mix alcohol with nitric acid, instead always mix the nitric acid with the alcohol. The reverse may result in a small explosion or a chemical reaction that causes the nitric acid to “pop”, this can be potentially dangerous. Make only as much nitol as it would take to etch just a few slices at a time. This will be plenty for one person to handle and would limit the liability during an accidental spill.
Start by pouring the alcohol into a small glass container. Never use a plastic container to mix the nitol, as the acid may be strong enough to burn through the bottom. Using an eye dropper add the proper amount of nitric acid to the alcohol. Once the alcohol and nitric acid has been poured and mixed it is ready to be used. Although it is possible to store the unused nitol in a closed glass container for later etching, it makes more sense to make only as much as will be used at one time.
Begin by placing the iron meteorite slice that is to be etched in a shallow glass container like a glass baking dish. Then using a small paint brush begin applying the nitol to the sanded surface of the meteorite. The technique is simple, just brush the nitol on one side and then turn the slice over and brush the other. A blackish film will appear on the slice as the nitol is being applied, each time the film is brushed away a faint etch will begin to appear. Continue the process brushing each side over and over until the desired etch is achieved.
Since each type of meteorite etches differently and at different speeds, experience is the only way a person will know when enough nitol has been applied, and when the etch is as good as it can get. To get a darker etch one may use a little more nitric acid in the mixture. A deeper etch would result when nitol is applied to the same slice for a longer period of time. Ferric chloride is used to achieve a more holographic look to the etch.
Ferric chloride or PC board etching solution as it is commonly called can be purchased at any Radio Shack electronics store. It is very inexpensive and costs about $5 per pint. Obviously used primarily in the etching of PC boards, ferric chloride can work wonders on a meteorite. However, over exposure to ferric chloride can promote the rapid oxidation of the newly etched slice.
Ferric chloride should never be used as a primary etchant, instead it should always be used in the same way spices are used in cooking. That is to say it should only be used to add highlights to a meteorite that has already been etched with nitol and then washed.
Ferric chloride is sometimes brushed on or may be dabbed on with a sponge, a holographic effect is produced when it is dabbed on. These two application methods of ferric chloride will produce a nice etch but will also over expose the slice thus making it unstable.
If an etch is deemed substandard after etching with nitol, or a darker more holographic etch is desired ferric chloride can help. Simply pour a cap full of ferric chloride into a “glad type” sandwich bag and then drop the nitol etched slice into the bag. Placing the baggie between the thumb and forefingers pat the sides of the baggie against the meteorite slice. Make sure to pat over the entire meteorite uniformly and quickly as the slice should be immersed in the ferric chloride for less than 5 or 6 seconds. This process should produce an amazing holographic effect without the worry of over exposure to the ferric chloride.
For even quicker results using ferric chloride heat up the meteorite with hot water from the tap before placing it inside the baggie. This will speed up the chemical reaction and produce the same effect within 3 or 4 seconds. This process should be done as quickly and carefully as possible, in part so that the ferric chloride will not have time to possibly leak through the plastic bag and stain everything in sight. When attempting this technique it may be a good idea to try it over a stainless steel sink.
A word of caution, never touch a meteorite without gloves during or after it has been etched. The acid on the fingers will immediately stain the meteorite during etching and will promote rust after it has been etched.
Once the desired etch is achieved with either ferric chloride or nitol the slice will need to be washed immediately. This is done by rinsing the meteorite slice in running tap water and then using Dawn dish washing liquid to form a lather. Rub the meteorite between the
thumb and forefinger, wash and rinse it several times to make sure it is rid of all the nitol. Since tap water contains chlorine the final step is to vigorously rinse the meteorite once again, but this time in purified water. When the washing and rinsing phase is complete, pat the slice dry using a soft paper towel.
An alcohol bath or oven heating of a freshly etched iron meteorite are two previously accepted methods for stabilizing that don’t work. Placing a meteorite slice in the oven to dry almost always causes a chemical reaction that will leave the once beautiful etch brown and tarnished. An alcohol bath for more than a few minutes will produce similar unwanted brown stains than wreak havoc on the etch.
Place the already etched, washed and dried meteorite slice on a cloth towel. Then using an ordinary hair drier continue to dry the slice, heat up one side and then the other. It won’t take long to heat up the slice so much so as to make it too hot to touch. For some reason this method almost never causes the meteorite slice to tarnish or take on a brownish hue.
When the meteorite has been heated and dried sufficiently place it in a small Tupper ware type bowl with a lid that has been filled with ATF (automatic transmission fluid). Gun oil or even automotive engine oil will also work as a substitute, but ATF seems to work best. Automatic transmission fluid seems to have a way of penetrating into the small cracks and crevices of the meteorite slice while chasing out any water. In this way slices can be carefully stacked upon each other for as long as necessary for the ATF to begin stabilizing the meteorite.
This technique works amazingly well, a meteorite can sit in the ATF for months if not years without any ill effects. Place the meteorites in the Tupper ware carefully so as not to scratch or otherwise damage other finished slices. The longer the meteorite stays submerged in the ATF the more it will seep in and inhibit rust. One thing is for sure it is very hard for rust to form around a well oiled surface.
In the past sub par methods as well as methods that just didn’t work have been used to attempt to stabilize an etched slice. Never use WD-40 or any other water soluble oils to try and stabilize a meteorite as water is often one of their main ingredients. Once rust has formed on an etched surface it is usually best to re-sand and start over. However, it is possible to remove the rust on an etched slice without re-sanding and etching.
Removing rust from an already etched meteorite is possible using a popular product called CLR (calcium, lime and rust remover). CLR can be purchased for about $5 at most any grocery or hardware store. While wearing rubber gloves, gently rub the CLR over the entire etched meteorite slice but concentrating mostly on the oxidized areas. The rust usually melts away, if it does, simply wash and rinse the meteorite as if it had been freshly etched. Then dry and store in ATF for as long as it takes to begin the stabilization. If the rust isn’t removed sufficiently then re-sanding and re-etching is the only option.
There is no way to cover every possible aspect of etching an iron meteorite. Experimentation via trial and error is half the fun of etching. Making something appear that was previously invisible to the naked eye is awesome to watch. Remember etching an iron meteorite is part science and part art, if the science is inspiring the art should be beautiful.