fire agate rough material 'how to' faq

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"Fire agate is a very beautiful,often mysterious and misunderstood stone...",
as most pulidors in the 'Agata de Fuego Capitol of the World' - Calvillo, will tell you.

We sell some of the best quality fire agate rough available on the internet, all of our material is handpicked for us by our minero amigo. Using his advise and 15 years of knowledge, along with our expertise on the web - together we formulate the value and decide the rarity of every fire agate we sell. In return, we share all profits with him and his family in Calvillo.

Once in awhile we experience problems with newcomers to the fire agate cutting and polishing world, and sometimes they are disappointed with their finished product or don't physically see any fire in the rough they purchase. Because they do not have the expertise in how the layers of color are formulated or the true hardness of the stone - this knowledge is very hard to come by for any lapidarist, because the miners don't share their secrets, nor do they public display some of their best specimens. (this occurs with the opal miners as well...)

Below are some tips about fire agate rough, and in the future we hope to continually add information here to help our clients to get the most out of their quality fire agate rough purchases from us here in México. Click here for cutting and polishing helpful tips and techniques.

split fire agate rough nugget
Agate cracked in half to reveal the fire found hidden within.

close-up of layers of fire
Visual layers of limonite which refract light into fire.
 
fire agate rough from 'mina negrita'
Solid black agate specimen from the Negrita mine.

hidden fire withing an agate specimenIf you do not see any visual fire, this does not mean that there is no fire in the rough material. Sometimes a specimen needs to be cracked in half (photo above left) to find the fire (photo left), or if you see lines (layers) in a sideview - this is the limonita, which is the refracted material that creates the illusion of fire (photo above middle).

We do not sell the mine floor sweepings you see at great discounts on eBay, we only sell good to excellent quality material, for amatuer and professional lapidarists alike. Because of our commitment to our miners, we do not accept returns for any rough material sold. We know you will get at least double your money back (minimum) from your rough purchases, but it is also possible to make 10 times the value of your original investment as well, on our high grade rough.

As new veins of fire agate in the rock are found, prices and quality can fluctuate - sometimes the miners will not give us their very best rough material because they know that they can make alot more money by polishing it and selling the cabochons themselves. But when there is a new strike, we can usually get them to part with a kilo or two of their high grade rough for us.

agate with quartz inclusions Sometimes you will find quartz-like inclusions growing inside of a fire agate raw specimens. The sprays of needles are inclusions of sagenite. These multicolored sprays are highly prized and sought after rare specimen by collectors, and not found in all fire agates. On average we only come across a couple fire agate rough with inclusions per every 15 or 20 kilos of material we receive from the Calvillo mines - about as uncommon (but not as rare) as 'lluvia negra', black rain fire agate.

 

Sometimes your material may look like it has a black coating (photo above) with no visible fire, these specimens are from the 'Mina Negrita' high up in the Sierra Mountains. Known for some amazing gems, the agate from the 'Negrita' mine is black agate and offset by the fire to make a striking gem. (see photos below)

imperial fire agate gem

fire agate high grade gem stone

 

WE WILL CONTINUE TO ADD TO THIS FAQ AS LONG AS NEW QUESTIONS OR PROBLEMS ARISE

FIRE AGATE CUTTING & POLISHING INFORMATION
Inside Every Fire Agate Is A Hidden Treasure...

Unfortunately Alot Of Stones Are Destroyed By Cutters That Are
Unfamiliar With The Nature And Formation Of Fire Agate.

how to cut and polish fire agate

Always Look For The Hidden Potential, The Treasure Is Waiting For You...

 

Fire Agate can be intimidating to the professional and amateur cutter alike. Fire agate ranging in color from clear to dark brown and the layers of the iron oxide minerals limonite or goethite that interact with white light to create the "fire" or iridescence. There is usually a milky translucent chalcedony that marks the stone's top. The characteristics of rough fire agate can vary considerably, depending on the mine and source material.

Fire agate is deposited in botryoidal form, meaning the structure resembles bunches of grapes, commonly called 'bubbles' or 'bubbly'. Most pieces of fire agate rough are twisted and deposited in a variety of angles. This creates a challenge for gem cutters because the sought after color layers follow highly irregular contours in the underlying brown agate. The art of cutting fire agate lies in finding the brightest, best-colored layer and following its contours wherever they lead and not cut through the iridescent layer itself. Sometimes a slip in cutting reveals an even better color layer, but more often, the stone is completely ruined.

bubbles of fireThe 'bubbles' in fire agate vary tremendously in size, from almost microscopic to single large bubbles that can be in the 15mm range or larger, and in some rare cases, a lot larger. Generally speaking, the kind of rough displaying larger "bubbles" is best suited for cutting on standard lapidary equipment, because these shapes are easier to work on flat grinding and sanding surfaces. Fire agate with intricately contoured, irregular or 'bubbly' color can only adequately be shaped using gem carving techniques. Standard lapidary equipment is suitable for cutting most types of fire agate, be careful and take the time to carefully study how each stone is laid out by mother nature.

Most lapidarists prefer to cut directly from rough specimens, but occasionally excellent window polished material is available at reasonable prices. Naturally you pay a premium for someone else's knowledge and labor in doing the main work for you. Most window polished specimens often don't make good material to cut through, and only small stones can be cut from what remains of the pre-polished window.

The gemmy layers vary in thickness, with the brightest and best layer often at the point between the chalcedony and the brown agate material. Sometimes these layers are only a 1000th of an inch thick, and they are best cut by leaving a slight amount of clear chalcedony over the top as protection if possible. If you sand right down to the color layer, there is a good chance that sanding and polishing can destroy it.

In better quality rough, the color layers are arranged successively so that cutting through one layer reveals another. Or there may be multiple bands of layers ranging from very thin to reasonably thick. The gamble is deciding which is the brightest and most desirable color layer and to make it the top of your stone. Color layers usually run in succession from bronze to gold to red and then green, with the rarer blues and purple colors to follow (if they exist).

CUTTING: Wet and inspect your rough under magnification in bright sunlight. Look it over as closely as possible. If you can see through the chalcedony, try to find flashes that indicate color layers. Don't be disappointed if you don't see any color, it may still be there but you'll have to work harder to get to it. Next, carefully examine the edges of the brown agate at various angles in the light, searching for layers or flashes of color.

fire agate rough preparationSome rough comes without the chalcedony "cap", so it's easier to evaluate. But usually the first step in cutting is to eliminate the chalcedony. If it's thick, some careful trim-sawing can save a lot of grinding. But never cut into the dark agate layer! Removing this "cap" is hard work, tough on equipment and sometimes fruitless: lots of good looking rough turns out to be your basic garden rock. But there's no way to tell for sure until enough of the cap material has been reduced to allow any colors from underneath to be seen.

Direct sunshine makes it possible to do some very accurate grinding; indoor lighting, including quartz halogen floodlights, despite their intensity usually lie about the location and brightness of color planes within the rough. Being able to really see what you're doing is the single most important factor in cutting this stone.

It's the nature of most fire agate cabs to require some contouring to follow the color layers, and flat grinding wheels are designed to cut convex or flat surfaces. One of the toughest jobs is to grind into the chalcedony crevices and valleys between the larger individual bubbles areas. Unless you decide to invest in specialized diamond wheels shaped for this job, the only way I know to do it is to use the edge of the grinding wheel. Begin grinding one hillside first, then change to the other edge of the wheel to do the opposite one. You'll discover that, with care, the face of the wheel does all the work and the edge gets very little wear.

CAUTION: But this type of cutting can be very dangerous as well. The wheel can grab the piece of rough (and your fingers). Work very cautiously, bearing in mind also that putting pressure on the edges of most standard diamond wheels can quickly ruin the wheel. Work carefully, and never use excessive pressure.

grinding fire agate rough materialWhen grinding has proceeded far enough that vague brown shapes can be seen through the chalcedony, iridescence should be visible as well. Before there's any real danger of grinding into it, move from the grinding wheel to an expandable rubber sanding drum fitted with a 100-grit silicon carbide belt for wet-sanding. Instead of aligning the sanding belt evenly with the outer edge of the drum, pull it about 3/8-inch past the edge. After you start the drum rotating, this fold-over area provides for contour sanding and works very well if used with lots of water.

Use the edge of the sander to smooth out crevices and concave areas, and its face to work larger, flatter portions of the stone. You'll quickly discover that frequent sanding is the key to seeing where you're going in the grinding process. Grind a little, sand and inspect carefully in good light (sunlight, if possible). Repeat until the desired fire colors are fully revealed. The color layers are thicker on top of the bubbles and thin down on the slopes and edges, so do most of your initial sanding on the top.

FIRE AGATE TELLS THE LAPIDARIST HOW IT SHOULD BE CUT

deadspots in fire agateDon't try to force it into any particular shape - if you are uncomfortable with anything but symmetrical shapes or intend to cut only calibrated sizes for standard mountings, you may find fire agate very frustrating. It doesn't adapt easily to this style of cutting unless you don't mind wasting alot of color and being satisfied with what some call "brown-edges" or "deadspots"; a pool of shimmering fire surrounded by an ugly dead area of plain brown agate. Sometimes this style of cutting is unavoidable, but if you let the patch of bright color define the edges of the finished stone, you will end up with a much more pleasing and higher value stone.

Often, stones that showed only minimal color and brightness in the bronze and gold layers are capable of being turned into extremely brilliant and valuable multicolored gems, by having the patience and courage to stick with the sanding. There is no feeling more exciting than having a boring bronze stone suddenly start showing amazing colors of green, purple and blue, mixed together with reds, yellows and oranges.

Sometimes you win, but more often you lose... if you have reason to suspect that multiple or brighter color layers could be present in the underlying layers it is well worth the gamble. You usually end up with more boring or golden stones than you ever wanted anyway, so sometimes it is better to "Go For It!" and try for the the reds and greens and purples!

FREEHANDING: This technique is used by our 'pulidor' (polisher) and many of the old timers as well, that don't believe in dopping sticks. The stone is balanced between thumbs and forefingers (palms facing up) and gently moved against the wheel from underneath. Keeping the wrists straight, the fingers can act as a support pressing the stone to the wheel. Use the same light touch that you would use on opal, allowing you to remove only the smallest amount of material at a time, so that I don't grind through a fire layer and into an area void of color.

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