BY SARA M. SANFORD

Matching finger size to ring size is made a much easier task with the help of ring sticks (left) and finger gauges (right). Photos courtesy Stuller.

By and large, if you’ll pardon the expression, jewelry making requires a firm idea of how big things are. We need to measure the metal we work with: the length of a wire, the thickness of a sheet, or the weight of casting shot. If we work with gemstones, we need to know dimensions and carat weight. When casting, we need to accurately measure investment and water. Last but not least, we need to measure the people for whom we make jewelry. Whether we function mostly by guess or by golly, or prefer three-decimal-place precision, there are a number of tools which make measuring relatively easy.

However, sometimes it seems like learning a foreign language — do you speak millimeters? What is that in pennyweights? Could you give me that in grains? There are several measuring systems commonly used in the jewelry and lapidary fields. Which ones you use depend to some degree (pun intended) on where you live, and what the tradition is among those you learned from. With instantaneous worldwide communication now available, some of the older and more awkward systems (ligne, douziemes) are fast becoming extinct, and I doubt they will be mourned.

The United States is the last holdout against the metric system. Those of you who live, or have traveled, in Canada recently have already made the transition from miles to kilometers. But while there is a lot of resistance in the U.S. to dumping the old miles, yards, inches, fractions of 64ths, etc., international trade is pressuring U.S. industries, and eventually sanity, otherwise known as the metric system, will prevail.

The following article will help you wade through some of the confusion. But first a word on spelling. For some reason, several major manufacturers of measuring tools insist on spelling “gauge” as “gage.” This might be fine if you are discussing a pledge or token, a variety of plum, or marijuana — all dictionary definitions of “gage.” The very last listed definition of gage does list it as an alternative for “gauge,” but we’ll stick to the preferred version, and include the “u.”

EASURING SYSTEMS. There are two standard systems for measuring physical dimensions (length, etc.) and weight — English and metric. The traditional English system of miles can be subdivided into furlongs, chains, rods, fathoms, yards, feet, and inches, and the inches into halves, quarters, eighths, sixteenths, thirty-seconds, sixty-fourths, and even smaller, thousandths. It can take a degree in higher mathematics — or at least a calculator — to do any calculations. This system is a mishmash of measures dating back to Babylonian and Egyptian times, with numerous contributions from the Romans and Vikings.

Deluxe ring and finger gauge set. When measuring a ring set with a faceted stone, be sure to use a grooved ring stick. Photo courtesy of Stuller

The English weight system is even more confusing, since it is divided into two separate and definitely not equal systems: avoirdupois and troy. Most of us are familiar with the avoirdupois system (if not the name): this is what we see when we step on the bathroom scale or buy a box of cereal. The troy system, however, is used for measuring precious metals, and is divided into pennyweights (abbreviation: dwt!?!) and grains (not to be confused with a pearl grain, yet another weight system).

The metric system, on the other hand, is based on the decimal system, and everything is divided into 10, 100, or 1,000 units: meters for length, grams for weight. Prefixes based on Greek numbers — deka (ten), hecto (hundred), kilo (thousand), mega (million) — are used to designate larger amounts. Latin prefixes — deci (1/10), cent (1/100), milli (1/1,000), micro (one millionth) — are used for smaller measurements. Thus, a millimeter is 1/1000 of a meter, and a kilogram is 1,000 grams. Logical, sensible, and easy to use!

The metric system is relatively new, devised just after the French Revolution in 1795. In 1790, Congress refused Thomas Jefferson’s request that the U.S. adopt a similar system based on the decimal system. But conversion to metric is inevitable. Already we see dual measurements on the packaged food in the grocery store, or in the case of soft drinks, liter containers. The automotive industry is mostly metric now, as are many other industries, especially those with manufacturing facilities overseas.

To help with all this confusion, and to convert from one system to another, there are innumerable measurement comparison charts. Most jewelry technique books and some tool catalogs will have various charts, and people who deal with measurements daily, such as engineers and machinists, have handy pocket-sized reference books. But a word of caution: not all comparison charts are created equal. In consulting several different charts, I was informed that 5/32" was equal to .156, .1562, or .1563 inches, and was either 3.9687 or 4.0 millimeters in length. According to these charts, 18-gauge measures .040, .0403, or .040303 inches, and is either 1.0, 1.02, or 1.024 millimeters thick. Yes, the differences are very small, but they can be crucial. When converting troy ounces to grams, I used to multiply by 31.1, but now use a multiplying factor of 31.103. Again, the difference is tiny, but try it and see for yourself the difference it makes.

Finger gauge, by Stuller

OOLS FOR MEASURING. The level of sophistication in measuring is matched by the level of precision in tools. You may not need to know the length of a wire to the exact thousandth of a millimeter, but the more finely divided your instruments are, the more accurate your measuring will be.

Trying to cram an 8.2 mm x 10.3 mm cabochon into a premade 8 mm x 10 mm bezel cup makes a simple and effective case for accurate measuring.

As always, buy the best-quality tools you can afford — and you really can’t afford cheap ones in the first place. Why bother to measure anything if your measuring instrument isn’t accurate? For instance, avoid purchasing plastic measuring tools — both metal and gemstones are harder than plastic, and will damage the measuring instrument sooner or later, making it inaccurate. For my money, one of the top-quality tool manufacturers in this country is the L.S. Starrett Company, who have been in the measuring tool business since 1880. Their products are a bit expensive, but I think they’re worth it. Check out their Web site (www.starrett.com) for an authorized dealer in your area.

The most basic measuring tool is the ruler, also called a rule. A good quality, 6" (150 mm) steel ruler is an essential studio tool. It should, of course, have both English and metric graduations: inches, in 32nds, on one edge, and half millimeters on the other. Buy a ruler with machined divisions, not printed. A steel ruler is always better than a plastic or wooden one — you can use it as a straight edge, running an X-acto blade along it without cutting into it, as well as using it to draw a straight line with a pen or scribe.

Determining thickness, end-to-end measurement, or inside dimensions calls for a caliper, which range from a simple pocket model to digital models. Photo courtesy Stuller.

A ruler is fine for measuring something in a straight line, but not when you need a thickness, or end-to-end measurement. This is a job for the caliper, which can also measure an inside dimension, such as the interior of a tube. There are a number of calipers available, from a simple brass pocket caliper to a high-tech digital-readout model.

Pierre Vernier (1580-1637) was a French mathematician who invented the vernier system of subdividing graduated measurements. This allows a more accurate reading, by dividing the primary scale of measurement into further, smaller degrees of measure. With a vernier caliper, you can divide inches into thousandths, and millimeters into hundredths. But as always, the accuracy of the measurement is directly related to the quality of the measuring tool.

Similar to a caliper is the micrometer, usually used to measure dimensions less than 1", and to ten-thousandths of an inch, or hundredths of a millimeter. Micrometers are used primarily by machinists, who need to work to very small tolerances.

Another essential measuring tool for jewelers is the sheet and wire gauge, for measuring the thickness, or gauge, of metal sheet and wire stock. But before you purchase one, be sure it measures in the system you need. There are several systems, and of course, they are not correlated. For instance, 18 gauge in the commonly used American, or Brown & Sharpe, system equals .040303 inches. But in the English, Birmingham, or Stubs iron wire, it is .049 inches. Then there is the Washburn & Moen system, where 18 gauge equals .0475 inches; in W & M steel music wire, 18 gauge is .0395 inches; S & W’s 18 gauge is .041 inches; Stub’s steel wire gauge (as opposed to the iron wire system) lists 18 gauge as .168 inches, and the U.S. Standard gauge for sheet and plate iron and steel measures 18 gauge as .050 inches. Are we confused yet? Luckily, most of the sheet and wire gauges available through jewelry and lapidary supply sources will be the American, or B & S system. But beware if you get most of your tools from yard sales or junk stores.

Sheet and wire gauges are typically round discs of thick steel sheet, with slits cut into the perimeter to measure the thickness of metal. Usually one side is stamped with the gauge numbers, while the other side has the thickness in thousandths of an inch, and it will have sizes from 0 to 36 gauge (.325" to .005"). By the way, it is the slit which is the accurate measure of the gauge, not the hole at the end of it!

For gems, you can use a caliper or micrometer to measure unset stones. But to estimate the weight of set stones, there is also the Leveridge gauge, a millimeter gauge (to 1û10 mm) and weight estimator. It features a large dial, which is very easy to read, and it comes with a reference book to calculate the weight of diamonds. It also has multiplying factors for a limited number of colored stones, plus Akoya pearls to 12 mm. A less expensive system is the Jo-Di diamond weight gauge — a caliper with a reference book of estimated weights.

A diamond and stone gauge is made for measuring the size of loose stones and settings; most gauges come with an accompanying book to calculate the corresponding weight. Photo courtesy Stuller.

There are other tools handy to measure the size of gemstones and mountings; some even have fancy shapes in addition to rounds. Most of these are made of aluminum, with different-sized round discs representing the stone sizes, or holes cut into the aluminum sheet.

For design purposes, the meleemeeter system has many shapes and sizes of stones printed on clear plastic, to aid in rendering designs, or checking wax models.

There are two other measuring tools which can be handy to have — a drill gauge, and a bur gauge. The drill gauge measures the size of a twist drill bit, which can be used to determine what size bit to use for a specific size of wire, or to order a replacement for a worn drill bit. Incidentally, here is an example of why accuracy in measurement is important: 18-gauge wire is often listed as .040", or the same size as a #60 drill bit. But in reality, 18 gauge is .040303", which explains why 18-gauge wire is almost impossible to insert into a hole drilled with a #60 bit. Therefore, “rounding off” a long number can prove deceptive.

Drill gauges are rectangular sheets of thick steel, with holes representing various drill sizes. A larger drill gauge measures drills from #1 (.228") to #60 (.040"). Also handy is the smaller drill gauge, which measures from #61 (.039") to #80 (.0135"). A word of caution in using drill gauges — they are (or should be) made of hardened steel, and careless handling can damage or even break drill bits.

The bur gauge is perhaps not really essential (although for us tool junkies there is no such thing as an unnecessary tool). In some catalogs you will see burs listed by two to four different numbering systems, including both a metric size in millimeters and the English system size in thousandths of an inch. The traditional size number, usually from 9/0 as smallest through 40, the largest, is a relatively arbitrary numbering system, and has resulted in some odd sizes, such as 6 3/4. Often you will also see the ISO number, a standard set by the International Standards Organization which helpfully corresponds to the millimeter size of the bur. Thus, a #5 bur is also an ISO #016, and therefore is 1.6 mm in diameter. In fact, some catalogs have discontinued listing anything but the millimeter size, which is fine unless you need a specific size bur and only know that it needs to be .0622" in diameter. Of course, you can whip out the old calculator, track down the appropriate conversion table, and reckon away to find the equivalent millimeter size.

EIGHT. Once you have the length, width, and depth measurements covered, you might need to know how much your metal and/or gemstone weighs. Since jewelers and lapidaries generally work with such small items and minuscule quantities, our standard bathroom, kitchen, or postal scales are not nearly accurate enough, especially when a lot of money may be riding on a small difference in the weight of either precious metals or expensive gemstones. Investing in one or more good, accurate scales will save both money and time.

Because jewelers and lapidaries work with such small items and since a lot of money may be riding on a very small difference in weight, scales must be specialized and accurate. Electronic scales can weigh in either grams or carats. Photo courtesy Ohaus.

First, you have to decide on which weight systems you need. The traditional system for precious metals is the English troy system, which measures in pennyweights, with 20 pennyweights to the ounce, and 12 ounces to the pound (which is not equal to an avoirdupois pound). A pennyweight can be further broken down into 24 grains. Luckily, all but the most diehard traditionalists have abandoned this complex system, and are now using the metric system of grams. For measuring metal, a gram scale with an accuracy of 0.1 gram is adequate.

If you use a lot of gemstones in your jewelry, or cut a lot of stones, you will need a good carat scale. Because a very small difference in weight can mean a large difference in dollars, a carat scale with an accuracy of 0.01 carat is essential. There are five carats to a gram, and the gram scale can be used to weigh larger amounts of gem material, such as rough. But most gram scales will weigh only to 0.5 carats, not enough fineness when working with expensive gems.

CALES. There are three basic types of scales — balance, fulcrum, and electronic. One of the balance scales is the old-fashioned kind, with two pans suspended from a pivot point. You put the item to be weighed in one pan, then pile premeasured weights into the other pan until they balance. Total up the weights, and you have the weight of your metal or stone. This system has both advantages and disadvantages. The main advantage is that it requires no power. It can be used anywhere, without worrying about dead batteries or if there is an electrical outlet handy. The main disadvantage is that it takes quite a bit of time to transfer weights in and out of the pan until it balances. Then you have to add up all the weights to arrive at a total. Plus, it is only as accurate as the weights you use, which can be easily distorted through wear; and the smallest weights are easily lost. Balance scales are available with a capacity up to about 100 carats, or 4 troy ounces.

The other type of balance scale has only one platform or pan for the material being weighed, and then a series of notched “beams” with printed scales, and indicators which slide along the printed scales on the beams until a balance is achieved. Commonly called a triple beam balance, this is a good choice for weighing metal, especially larger amounts and larger sizes of sheet or wire stock. With optional attachment weights, the capacity of the triple beam scale is 2,610 grams, or over 80 ounces, and an accuracy of 0.1 gram. One of the major manufacturers of triple beam balance scales is Ohaus, a long established company with a good reputation for high-quality products.

A triple beam balance scale is a good choice for weighing metal, especially larger amounts and larger sizes of sheet and wire stock. Photo courtesy Ohaus.

The fulcrum scale is the least expensive, and consequently the least accurate, but is handy for quick measurements where exactitude is not required. It comes in either a gram or pennyweight system, but there is at least one model available with both, plus yet another with interchangeable indexes for both troy and avoirdupois ounces, grams, and even a postal scale. None has a capacity greater than 100 grams.

While electronic scientific scales have been around for a long time, they have been (and still are) very expensive. Fulfilling scientific requirements of accuracy down to a thousandth of a gram doesn’t come cheap. Most will have an enclosed platform, since a slight draft, or even your breath, will cause the scale to fluctuate. These scales can be programmed to weigh in many different systems, including grams, pennyweights, and carats.

However, with the development of miniature electronics, small and relatively inexpensive electronic scales are now available. Before you purchase one, think about what capacity you might need. If you work with mostly small, faceted stones, a scale with a maximum capacity of 50 carats will probably suffice, unless you do production work and buy large quantities of gems. On the other hand, if you work with large stones, or purchase large lots of stones or rough, you will most likely want a larger capacity, of at least 100 carats. Ohaus, Acculab, and Dendritics are all companies that produce electronic scales, for weighing either grams or carats, and some (more expensive) scales are available with both systems.

Regardless of whether you produce one or two pieces a year or do mass production, you need to know the weight of the metal for each piece, and the weight of any stones you use. These days, consumers are becoming better educated about quantities and qualities, and often want to know what the carat weight of a gemstone is. And of course, we all keep accurate records of each item we make, don’t we???

For those of us who do a lot of lost wax casting, a scale to weigh investment is a good idea. Accurate measuring of investment, and the corresponding amount of water, is necessary to maintain a proper ratio of investment to water, which will help to insure consistent results. The scale need not be accurate to 0.1 gram, but just to about an ounce. Yes, this will most likely be in the old-fashioned English (avoirdupois) system, but newer scales will come with a dual weight dial, marked in both pounds and kilograms. To complement this scale, you need a measuring cylinder, or pitcher, which measures liquids in cubic centimeters or milliliters. (One cubic centimeter equals one milliliter.)

EASURING PEOPLE. Most of us make our jewelry to be worn, and people are wonderfully diverse in their infinite varieties of size. So we also need tools to measure the people for whom we make jewelry. The most common tool is a set of ring sizes or finger gauges: numerous metal or plastic rings of specific sizes, in half size increments, gathered on a larger loop of metal, or a chain. Most come with sizes 1 to 13, or 1 to 15. (These sizes are United States standards, and do not correspond to European sizes.) If you do a lot of rings with wider bands, there is a set of wide-band finger gauges, since wide bands need to be made a bit larger in order to fit comfortably.

Moving up from the hand, there are a couple of bracelet size gauges available. This can be very helpful when measuring a wrist for bangle-type bracelets, to be sure they will slip over the hand without causing pain. It can also help in sizing a link-type bracelet.

Most of the rest of “people” measurements can be done with a string or a tape measure. But there is a handy neck chain gauge, which will indicate where standard lengths of chain, 16" to 30", fall on a client’s body. Depending on how thick a person’s neck is, the same length of a chain can have a quite different appearance on different
people.

One word of caution: never take a client’s word for granted on what size she/he wears. It will save you innumerable headaches if you confirm all measurements whenever you do a custom job.

THER MEASURING TOOLS. Sometimes we have to ascertain the size of an existing ring or bracelet, and of course there are tools which can help us do that. The ring stick, or ring mandrel, is a tapered length of wood, plastic or metal marked with U.S. standard ring sizes. (Technically, a ring “stick” is used only to measure the size of a ring; a “mandrel” is made of steel and is used to form flat ring stock into a band.) Just slip a ring onto the ring stick, and when it can’t go any further, that’s its size. However, if the ring shank is misshapen, you can’t get an accurate reading. A soft plastic ring stick will conform to an oddly shaped shank; or you can use your own body to determine the size: find a place on one of your fingers where the ring fits snugly, and then try on ring sizes until you find the one which matches the fit.

Another word of caution: if you are measuring a ring with a faceted stone set in it, use a ring stick or mandrel with a groove which runs the length of the tool. You can easily chip the culet of a stone if you force it onto a mandrel without a groove.

Several tool supply companies have a shank size and bracelet gauge listed, which will give you the length of metal stock for any size of ring or bracelet, plus measure the inside of a bracelet. But be aware that different gauges of metal stock will require slightly different lengths to make the same size of ring.

So, whether we measure metal or stones, casting investment or people, the more precise our measuring tools are, the more accurate our results will be. And therefore, the better our craftsmanship is. Which brings me to the last word of advice, borrowed from the woodworkers: measure twice, cut once.

Sara M. Sanford is a professional jeweler and a founding member and past president of the Creative Metal Arts Guild in Portland, Oregon..