Right Girdle Thickness
Right Girdle Thickness
This is a question that most new faceters have. Judging girdle thickness is generally something you get better at as you get cutting experience. But for some one who has not cut many stones or is just learning to facet, figuring out girdle thickness can be tough to do.
The first thing that people should keep in mind is. What is the girdle of a stone used for? The answer is fairly simple. The girdle is placed on a faceted gemstone so that the stone can be set in jewelry. There are some other reasons, but this is the main reason we faceters cut girdles, “to set the stone…” So what are the most important things that a girdle should have? Ideally, a girdle should be level, strong, and not too thin or fat for the stone to be set in jewelry. I know easier said than done for a new cutter. Remember I said the girdle was for setting the stone in jewelry? I think understanding the setting process will help a new cutter understand the larger picture and shed some light on girdle thickness. Look at the graphic below.
Typically the jeweler cuts a notch (sometime the notch is precut depending on the setting) in the setting prong(s) that is shaped to match the outline of the girdle of the stone as closely as possible. The better/closer the notch is to the shape of the stone/girdle, the better/stronger the setting will be when done. Once the notch is cut the jeweler gently bends the metal of the prong(s) around the girdle of the stone to hold it in the jewelry setting. So as you can see the thickness of the girdle is quite important when setting a gemstone.
If the girdle is too thick the notches in the setting prongs will have to be large and deep, often weakening the integrity of the prongs. If the girdle is too thin, the notches are small, will not hold well and more than likely chip the stone when the jeweler sets the stone. There is a fair amount of pressure applied to the girdle as the prongs are bent into place (also some jewelers have the finesse of a jack hammer).
Tip: Go to a local jewelr or jewelry supply store and ask to see some settings that are available. Blank settings (no stones) are generally widely available. Look at the prongs and notches on the settings and envision the girdle thickness you need. Remember that typically the notches need to be enlarged and fitted to the individual stone before setting. So the notches will be a bit different/larger than the original notches in the finding when the stone is actually fit into the notches.
Girdle observations and tips:
Always set your loupe down and look at the girdle of your stone with your naked eye… Examine it from a normal reading distance. Always looking at the girdle through a loupe will give you a false sense of size. A thin girdle will chip it’s just a matter of time, if the jeweler does not chip it when setting (they usually do) the person wearing the finished jewelry will sooner or later. Thin girdles are vulnerable and weak, a thin girdle to me is the most serious problem/mistake that a faceter can make when cutting a gemstone.
The easiest way to tell a girdle that is too thin is. Does the girdle look sharp, like it might cut you when viewed with your naked eye? Then it is too thin. A fat girdle will make the stone hard to set and provide poor purchase for the prongs that hold the stone to grip it (the girdle) when setting. Thick girdles are better than too thin, but generally not a good idea. Some cutters leave thick girdles trying to gain some carat weight when the stone has too much crown depth. This is generally not a good habit to get into. Believe me jewelers will not thank you for thick girdles. Cut the girdle to the correct thickness and charge a little more for the stone if you need to.
Does the girdle look roundish to your naked eye? Then it is too thick. An uneven girdle, will make the stone difficult to set level and securely, the notches on each prong around the setting will all have to be cut differently. An uneven girdle takes a lot of hours to set and will not make you a very popular person with the jewelers setting the stone.
Think that is not a big deal? I have actually sold my stones to many jewelers over a competitor’s because my stones had correct girdles and were easy to set. Time is money. Of course there are some stones that have a couple or all of the above problems, look for the “bald jeweler”, he has been trying to set these stones.
What about the designs and 0.02 thickness they call for?
You will notice that on almost all faceting designs, the calculated girdle thickness is .02, the formula is H/W= (P+C) /W+0.02 = depth of design. This is basically an arbitrary figure (2%) that is used by the program as a standard for doing calculations. In other words (my opinion), the 0.02 girdle does not really have much practical application in the real world. It is used for calculating designs and sometimes in contest cutting. But not a standard I worry about in my day to day cutting.
So how do you get a decent girdle thickness? Well here is a concrete way to visually see a girdle thickness using a gauge. There are other gauges and calipers (like spark plug gauges), but this one is a jewelry industry standard and not expensive to buy.
Left: Is an American Standard Wire & Metal Gauge. This gauge is marked 1 gauge to 30 gauge on one side and in hundredths on the other side.
This is a standard gauge in the jewelry industry and can be found in about any jewelry supply store. You may already have one if you have taken some jewelry making or metal smithing classes.
Typically if you were trying to identify the gauge of a particular metal or wire you would slip the metal in the slots on the gauge until you find a slot that is just snug, but not tight or loose. That would be the gauge (or measurement) of that particular piece of metal.
So how do you use it for judging girdle thickness? Well kind of the same way.
Left: Is a close up of the American Standard Wire & Metal Gauge and a piece of Aquamarine.
Note: The gauge I am using is metal, so I never really touch the girdle with the gauge. The metal gauge could chip the stone if care is not taken.
Note2: They do make plastic gauges of this type, which would be fine for this application, better than a metal gauge. The plastic gauges do not wear well when used with metals and around a jewelers bench with torches being used. (they usually end up melted or on fire).
Basically just hold the stone up to the girdle so that you can see the thickness of the girdle. The gauge gives a very good constant visual reference to judge girdle thickness by.
Left: Is a close up of the American Standard Wire & Metal Gauge and I have pictured the part of the gauge that I generally cut my girdles to. .020 to .040 is pretty much the range I cut all of my girdles to, of course on an extra large or small stone I may be a little larger or smaller depending.
The Aquamarine in the picture above is 9.2mm square and the girdle is about .025-.028 thick. This would be pretty close to my standard girdle thickness on average. I tend to cut stones that are 1-10 carat range and probably mostly 2-6 carats over all. Remember girdle thickness is not an exact science, and when you get some experience you will rarely use the gauge. Like I have said, judging girdle thickness is something you get better at as you get cutting experience. Just keep working on it and you will get the hang of it. Remember as a new cutter, err on the side of a little thicker girdle than a thin girdle if you can.