Goldsmithing: Stone Setting Techniques
The pleasure and challenge of including gems in a jewelry object (beyond the intrinsic beauty of the gem, of course) is to resolve the various factors that come into play. Well designed stone setting techniques must achieve several goals simultaneously – it must secure the stone, enhance both the gem and the metal object, it must stand up to wear while protecting the stone, and it should harmonize with the aesthetics of the piece.
One of the first decisions about incorporating a stone is to determine whether it is to be the focal point of a design or a component in service to some other more dominant aspect. Clear thinking on this fundamental question will assist in the many decisions that must follow, including proportion, style, texture, color, location and size.
This is the simplest of the basic settings. The stone sits on the base plate and is held by the perpendicular wall that surrounds the stone. This wall is pressed over the stone so that it leans against it, in this way securing it to the piece.
Bezels are most commonly used for cabochons, a gem shape that has a flat bottom. Because light does not usually enter a bezel set stone from behind, the setting is most commonly used for opaque stones.
The early steps in making a bezel are shown in figure 12.1. Cut a strip of metal, approximately .25 to .35 mm in thickness (27-30 gauge B&S), wide enough to extend over the curvature of the stone when set on its side. This dimension will vary considerably depending on the height of the stone; the taller the stone, the taller the bezel must be to properly secure it.
Form the strip around the stone so that it makes a close fit, then cut and prepare the ends to make a clean joint. In the case of rectilinear stones, use dividers to step off the various planes of the stone’s perimeter, adding a little bit to allow for thickness, then use pliers to make sharp corners. For unusual shapes like the one in figure 12.1c it might be worth the time to saw out a silhouette (or footprint) of the stone from brass sheet, then use this as a form against which the bezel can be adjusted.
The bezel is soldered closed with hard solder and checked against the stone to be certain it makes a good fit. The stone should not rattle in the setting, but it should not need to be forced in either. If the setting is too large or too small, it must be fixed or discarded and a new attempt made. A poor fit at this stage will not improve later on!
The bezel is soldered onto a base plate, preferably from below as the arrangement sits on a soldering tripod and screen. Alternately, binding wire may be used to secure the pieces in their correct position. When the solder has flowed completely, the binding wire is cut off and the piece pickled. Avoid the temptation to check the fit of the stone at this point – because no further mechanical action has been taken, there is no reason why, if it fit before, it will not fit now. It often happens, however, that a lingering flux residue or minor bending that occurs through normal handling will cause the stone to get stuck in the setting. For this reason, don’t insert the stone until you are ready to set it. The excess sheet is cut off with a saw and the edges are filed (figure 12.1b). The base plate is usually cut flush with the bezel, but there is no reason why it cannot be cut ornamentally.
Making a parallel walled bazel setting.
a) stone with frame and base plate, b) finished bazel, c) scored bazel for an octagon setting
This type of setting may be thought of as a backless bezel in that the holding aspect is a wall that completely surrounds the stone. As seen in the following illustrations, there are many variations on this setting – only the most basic are shown here!
Frame settings are particularly good for translucent and transparent gems because light can enter from the back side, but they can of course be used for opaque stones as well. In the case of parallel walled frames, an inner bearing is cut or added to support the stone; in the case of conical settings, the decreasing size of the form supports the stone from behind. In both cases there must be sufficient metal above the stone to press over it. This is what secures it in place. The thickness of the metal sheet must be determined for each case, and will depend on the size of the stone, the type of metal being used, and the nature of the jewelry item.
Cones and Pyramids
Figure 12.2 shows three different ways to make a conical setting; a fourth is presented in figure 12.3. As seen in figure 12.2a, a strip of sheet metal is scored, bent and soldered to make a parallel-walled square frame. Corners are cut from this, typically with a file, and are beveled so that they make a tidy joint when brought together. This frame is then soldered.
Constructing a conical setting from a parallel wall frame.
a) scoring, b) cutting, c) forging
The advantages of this method lie in controlled measurements, even metal thickness, and the fact that this does not require special equipment. A disadvantage is that the corners are brittle because of the solder they contain; this makes them difficult to press down over a stone.
A parallel-walled frame is bent as before, by scoring the corners and folding up the form (figure 12.2b). This is then set on an anvil or similar steel form and planished at one end, making sure to strike each of the four surfaces equally. This will stretch the metal outward, forcing it into a pyramid shape.
Note that it is necessary to start with thick metal, not only to allow for the stretching, but because there will be hammer marks that must be filed out.
A Striking die made of hardened steel can be used to shape a cone or fabricated square frame into a pyramid. Start with a blank that is equivalent to the center dimension of the intended form. The lower part of this will be compressed and the upper section will be stretched. The annealed blank is set into position, the corresponding die is slid into it, and the punch struck with a hammer (figure 12.2c).
The disadvantage of this tool is its cost, but for some studios this will quickly be covered by the efficiency of the operation. Particularly once an ideal blank has been determined by trial and error, this stamping die is both easy and quick to use.
Perhaps the most universally useful method is to fabricate the frame from sheet metal, following patterns like those shown in figure 12.3. The dimensions and shapes are first laid out on stiff paper to insure the correct fit. This is then transferred to sheet metal that is cut out with a saw. If a number of similar mountings are to be made, it’s a good idea to cut a copper or brass stencil of the form; this is more reliable and can be easily traced.
To layout a cone, first draw the intended shape in profile, or side view. Extend the lines of each side to locate the center point of a circle, seen in figure 12.3b. Set a compass point at this junction and strike an arc with the other point at the top of the cone. Repeat the process with the pencil end of the compass at the lower end of the cone – these two lines provide the outer dimensions of the blank that will be needed.
Diagrams of various constructed settings
To determine the length of the blank, calculate the circumference of the top of the intended cone by multiplying its radius times p (3.1416). Measure this distance with a curved ruler or a thread along the top of the arc, making marks at each end. Connect these marks with the center point that was used before and you will have laid out the exact pattern for the cone drawn in profile. In the case of metal (as opposed to paper, for instance) allowance should be made for the thickness of the sheet. While this can be calculated, on the scale of stone settings it is usually sufficient to simply add a small amount to the measurements made. This is especially possible in the case of a cone because if the setting is too large at one point, the stone simply drops down a tiny bit to find the place where it fits.
Use a similar system to lay out patterns for the pyramid and sloping hexagon shown in figure 12.3. Repeat the first steps – draw actual side view, extend sides to locate a center point, and draw arcs at the top and bottom of the form using that center point. Take a measurement of the top of the pyramid with the compass and step it off across the arc. Connect these points to each other and to the center point with a ruler and you will have the patterns shown. These are transferred, sawn, scribed, and bent. Though it appears there is an extra step, these forms are even easier to make than the cone.
Creating a bearing by
engraving (a) or adding an inner rim (b).
Making a Bearing
To prevent the stone from falling out the back of the setting, and at the same time to keep it level, a frame style bezel needs a bearing, or ledge, on which the bottom edge of the stone can rest. This can be achieved by carving a portion of the bezel away or by adding a piece of material (figure 12.4).
In both cases the bearing needs to be sufficiently wide to secure the stone, and perfectly level within the setting. The amount of material above the bearing must be sufficient to press down onto the stone to hold it securely.
When fabricating a bearing, an inner unit (cone, pyramid or tube) is made in the same way as the outer one, though typically it is slightly thicker. Fit is everything, not only to allow a proper solder joint, but to hold the piece in position during soldering. In a proper construction the fit is so tight it must be forced into place. This will insure that it doesn’t move as the solder flows. The solder chips are applied from the bottom and drawn up into the joint, the point being to avoid a build up of solder along the bearing.
When cutting a bearing, work can proceed with gravers, burs or a combination of both. In the case of a cylindrical mounting, a cylinder shaped rotary file is used to carve away a portion of the inside of the bezel. It will be obvious that the metal used to make the bezel must be thick enough to accommodate this. A flat or square graver is often used after the bur to even up the surfaces.
Stone setting tools
a,b,c,d) stone pushers, e) burnisher f) beading tool, g) millegrain tool, h) wax peg (for placing the stone)
When cutting a bearing into a conical setting the outward leaning sides mean that very little material needs to be removed. The primary purpose of the bearing in this case is to level the stone and hold it in position as the stone is set. By thinning the wall at a specific band, the metal is made easier to bend over at that point, in this case leaving a top edge that is attractively thick. Of course it must be noted that the bearing cannot be cut too deeply for fear of breaking through the wall. This bearing can also be cut with a Hart bur in the flexible shaft machine, in which case a graver might be used only to even up the walls of the groove.
Cutting a bearing into an oval cone is slightly more difficult though the principle is the same. The different radii around the oval require a more sensitive handling of whichever tool is used.
When the bezel is made completely ready, it is wise to check the piece one last time to be certain that no further soldering will be necessary. When you are certain, pick up the stone with a bit of beeswax and set it into the bezel, making certain it is level.
The top edge of the bezel wall is then pressed over the stone to secure it in place. Any of the tools seen in figure 12.5 can be used for this – most goldsmiths develop a particular favorite, though all would agree there are times when the surrounding shape makes one choice better than another. These tools are usually made of unhardened steel, though brass or bronze can also be used. The surfaces are generally polished, but the fine tooth left by sandpaper has the advantage of gripping onto the metal slightly.
In order to avoid a pucker of metal at any one point, it is important to distribute the compression of the bezel around the stone. To accomplish this, press the bezel toward the stone, then move the tool to a point directly opposite and repeat the process, again pressing the bezel only part way down. Move to a point equidistant between these two points and press it, then go directly opposite that. If we imagine the points of a compass, the idea is to press the bezel at north, south, east and west.
Check to be certain the stone is level and seated as far into the mounting as it can go, then proceed to press the points in between those just bent over (NE, SW, NW, SE).
When setting a rectilinear stone, press the corners in first. When the stone is securely set – it feels stable and makes no sound when shaken – polish and harden the bezel by rubbing it with a burnisher. If the bezel is irregular after pressing, use a flat file or pumice wheel to make the surface flat before burnishing. When using a wheel, run it against an old file to sculpt exactly the correct shape.
The top edge of the bezel, (the small rim where the bezel contacts the stone), can be polished with a flat graver or a felt buff. It is also possible to leave it matte with the pumice wheel, or to ornament it with tiny beads using a millegrain tool.
Using punch to cinch the bazel
Leading punch without the help of an assistant
In cases where a stone is very delicate or a bezel wall very thick, it is often easier to set a bezel using a hammer and punch. Though great care is needed, it is easier to arrest a hammer blow that is going wrong than it is to stop the muscular thrust of a hand-held bezel pusher.
The object is anchored by whatever method suits the studio and the stone setter: in the example shown in figure 12.6 it has been attached to a shellac (or pitch) stick. The first step is to secure the stone sufficiently that it won’t jump about as the bezel is being pressed over. Though tempting, glue should not be used for this because it makes it impossible to know when the bezel has been properly secured. If an adhesive must be used, a tiny film of beeswax is applied to the underside of the gem. This will minimize its movement, but still allow a discerning worker to know when the wax is all that is keeping the piece in place. Use conventional bezel pushers to move the bezel enough to touch the stone, at least at the four cardinal points. It will then be possible to switch to the use of a small hammer.
It is often easiest if the goldsmith has an assistant to strike the hammer blows, allowing the setter to hold the work and locate the tool. This is the situation shown here. Figure 12.7 shows the way a setter can use his or her little finger to press down on the stone while simultaneously holding onto the punch. In some cases a rubber band can also be used.
A motorized version of this process is made possible through a hammer handpiece, a specialty piece of equipment that converts the rotary motion of a flexible shaft machine to a back and forth stroke. In this case the operation is the same, but the machine is passed across the surface of the bezel, changing angles as the work proceeds to cinch the bezel down onto the stone.
A variation on this is called a mirror setting, so named because it presents a flat highly polished surface that surrounds the stone as if it was set into a mirror. This thick-walled bezel is particularly appropriate for stones with a large table, like the one shown in figure 12.8. A thick bezel is made and pressed over so that it completely covers the side facets of the stone. In practice it is best to provide a little excess metal, knowing it can be filed off later. When the metal is tightly pressed against the stone with a punch, the metal standing above the setting is taken away (do not use sandpaper!) and the surface is polished with pumice and a leather stick. After polishing, the stone will appear to have a shining mirror as its frame.
Another variation on a bezel is the “bowed setting” seen in figure 12.9. This is nothing more than a simple thin bezel in which the process stops after pressing in the first eight points. In a tall setting like the one shown, use a screwdriver or similar shaped punch to press the bezel wall at even intervals. When polished to a bright shine the convex shapes are highly reflective and make an eye-catching setting.
Framing an Irregular Shape
This variation on a bezel is less straightforward but sometimes the only solution, particularly when setting a panel of irregular contours. An example that will be used here is a shell cameo, and other uses include enamels, coins, found objects, etc.
Bowed bazel setting
a) sequence of work, b) finished setting.
Start by making a surrounding bezel in the usual way, making certain that the metal is thick enough to withstand the handling that is part of the process. When the fit is correct, solder the bezel closed and test the cameo in it, marking the orientation so it is repeated each time.
With the shell in place, scribe a line along the inside wall that follows the irregular contour of the piece. Remove the shell and cut away metal down to this line, using burs, shears and files. Make an inside bezel and slide it into the larger bezel, using the previously trimmed piece as a guide for filing the inner rim.
a) separate pieces, b) wall with inset cameo (side view), c) finished setting.
Make an oval of wire, solder it closed, and planish it out to make a flat rim. In the end, this is the element that will hold the stone from the front. Bend this as necessary to fit closely onto the top lip of the outer (larger) bezel. The detail at figure 12.10b might make the location of this piece more evident.
When all soldering and finishing is complete, the cameo is slid into the setting from the back and the internal bezel used to lock it into place. This tight fitting ring should make a friction fit all around the inside of the primary bezel. It is further held by rivets, engraved stitches, adhesive or tin solder.
We might think of a prong setting as an open-backed bezel from which segments have been removed at equal spacing around the rim. The advantage of prongs is that they allow more of the stone to show; in this way a prong setting resemble the way you might hold a coin by its edges to show it to a friend. The disadvantage, not surprisingly, is that the fingers of metal are prone to snag on fabric, and can be bent back more easily than can a bezel.
Variations on prong constructions are as numerous as the shapes in which stones are cut. A few examples are shown in figure. 12.11, but these should be taken as only a glimpse of the many varieties that can be made. And keep in mind that each of these styles could be altered in proportion or metal to create several settings!
As mentioned above for frames, the bearing for a prong setting can either be added on or cut from the material itself. In those cases where an interior bezel is to be added, the upper edge must often be filed at an angle to properly fit the pavilion (underside) of a faceted stone. This situation is illustrated in the upper right corner of figure 12.11.
Square prong setting
a) vertical walled prong setting, b) and c) conical prong setting, d) conical prong setting with split frame, e) special form of a square prong setting.
a) file grooved prongs, b) prepared chaton with foot ring support.
This important setting, shown in figure 12.12, is a staple in the jewelry industry, and shows clearly how bezels are similar to prongs. If you can mentally “fill in” the scooped out openings in figure 12.12a, you will see how much it resembles the bezel shown at figure 12.4a. It would be a worthwhile exercise to set two identical stones in settings like these – the effort would show that while both are attractive, the effect of the bezel is to present a framed gem, while the prong presents the gem itself, ideally floating in the jewelry piece.
Though crown settings are commonly used today to set diamonds in ladies engagement rings, this is somewhat risky, given the ease with which prongs can wear down or be accidentally pried open. It is important to use metals and alloys known for their toughness when setting diamonds in prongs!
The construction of a crown setting starts with a cone of such a size that the stone fits part way into it. The cone is shaped on a mandrel and filed to uniform symmetry. It is possible to cut the bearing groove at this stage, though some goldsmiths prefer to wait until after the prongs have been cut out.
The upper edge is sanded smooth and divided with a compass or template into the chosen number of prongs, typically 4, 6 or 8. After drawing a guideline around the cone about one-third of the way up from the bottom, a saw or file is used to cut away material from between the prongs. In a small setting, this is all that is required, seen in figure 12.12a. In larger settings, the cone is inverted and a knife-edged file is used to remove material in a position staggered from the location of the prongs as shown in 12.12b. This will visually lighten the setting. For strength the lower tips are soldered onto a ring made of flattened wire. Alternately, this piece may be made by soldering the prong onto sheet or by making the cone a little long, cutting the lower piece away, then reattaching it after the filing is complete.
The setting process is even easier than with a bezel because there is less metal to be moved. If the bearing has not yet been cut, it is made now, using a bur, a graver, a file, or some combination of all three. The particular action will depend on access to the setting, the number of prongs, the size of the setting, and the tools at hand.
After removing any last burs or flaws in the mounting, the stone is pressed into position and checked to see that it touches each prong. If not it is removed and the prongs adjusted accordingly. The prongs are next checked to be certain they are the proper height, and if necessary they are cut down and shaped with files. Each prong is then pressed over the stone part way, the stone is checked to be certain it is level, and the prongs are set down firmly onto the stone. The tips of each prong are hardened and burnished with a burnisher or a beading tool.
When doing repair work it is best to remove all stones from their settings. It is clearly most efficient if this can be done without harming the setting so it can be used again, but it often happens that a piece old enough to be brought in for repair is also sufficiently worn that the settings will need to be replaced. This can be a big job all by itself, so be certain to examine the settings while the customer is still on hand so you can inform them of this possibility.
In removing stones, remember that every stone, even those considered hard, should be treated with great care. Always work over a table, leather bag or sweeps drawer to catch the stone in case it is dropped.
Use a sharp, pointed knife tip as a wedge, easing it in between the bezel wall and the stone. Always direct the force against the metal rather than the gem, and be patient, moving slowly around the bezel. For small stones, a steel needle or dental tool can be shaped to a narrow chisel shape for this purpose.
The hardest part seems to be in finding a starting point – it’s possible to feel your way around the stone several times before the tip of the tool finds a point of entrance. Ease into this place and work from there around the bezel, always avoiding force and a levering motion. Pulling too hard on any given point not only endangers the stone but also pulls the bezel on the opposite side of the stone tighter. Continue going around the stone until the bezel is peeled back enough to allow the stone to be shaken out.
This method will not work for thick bezels; instead, use a saw to cut into through the bezel at one or perhaps two places. Insert the tool there and pull the metal outward. It is possible to repair these cuts by soldering a thin piece of metal into the cuts, but in some cases it might prove easier to make a new bezel from scratch.
Lifting prongs is considerably easier than removing a stone from a bezel. Set the knife blade flat on the crown facet of the gem and slide it down to the girdle of the stone. The prong lifts quite easily. It is also possible to purchase a prong lifter, a rectangle of steel into which are cut into slots of various sizes. This can be used like a miniature crowbar to peel the prongs open.