Setting. Jewellery Settings and Platinum. Setting and Mounting Techniques. Manual Index

Transcription

1 6 Jewellery Settings and Platinum Setting and Mounting Techniques Manual

2 6.1 Jewellery Settings and Platinum Platinum is regarded as the best available material for gem settings, particularly for diamonds, both on the grounds of complementary colour and high strength in thin sections such as claws and collets. The most notable feature of platinum is its ability to dead set, meaning that it stays very firmly where it is put and neither springs back nor sags. Although white golds and platinum alloys have improved in the last 40 years platinum jewellery alloys still have the better combination of strength and ductility. Modern design and fashion, particularly where "only the best will do", has extended platinum use not only to settings for other white stones but to virtually all gem quality coloured stones too. It is not surprising that in countries where a white precious metal is preferred, the whole piece is made up in platinum alloy. Design has developed to include other precious metals alongside platinum for attractive colour contrast reasons where marking regulations permit; not as a cheap substitute. So, the original good setting characteristics of platinum now support a much wider range of designs. Making Settings - Design Consideration Because of the relatively high strength and stiffness of platinum, claws, bezels and collets of fine section are stronger than expected on first experience. Settings in platinum need not be heavy unless that is a desired design characteristic. For instance, wire no more than 0.6mm diameter is sufficient for claws to hold stones up to a third of a carat and shaping from 1mm wire is about right around one carat. Different grades of platinum alloy may be used in the same piece. For instance, a setting for a delicate stone such as an emerald may be combined with a hardwearing shank and/or an ornate complex cast shape; all joinable after finishing as individual components. All of the hallmarkable platinum jewellery alloys are equally suitable for different types of settings and the final choice may depend on the design of the rest of the piece. If the designer wishes to take advantage of the finer points of difference: Pt-palladium alloy is a little softer for opals, emeralds and similar "soft" stones. Pt-copper alloy is better for raising grains and pavé work. It usually gives the best colour match with solders. Pt-cobalt alloy is best for complex as-cast settings but it also retains good claw setting capability. Shanks in any of the three alloys are good for stretching up to size. The shaping of platinum for jewellery has been dealt with under "Handworking" and there are no unusual problems in making settings by hand. Ideally, the metal within the setting should be left in a partly work- hardened state. However, it is now possible to make or buy stamped or precision cast settings in standard sizes, with bearer and setting areas already partially shaped, or more complex special shapes with remarkably good surface finish as-cast. Even a cast setting is worked slightly when being cleaned up, trimmed, eased into position and burnished. With a little preplanning, it is possible to confine the annealing effects of soldering and welding to near the actual joint and rely on residual workhardening further away for useful additional strength in, for instance, the tips of claws. If there is doubt about the continuing ability to work the setting without cracking thin sections, start with material in the annealed state. Always get as much of the finishing to size and polishing done before assembling the setting. Even soldering, welding or annealing after that stage does not oxidise the metal and it is all the easier to finish the assembled piece, including the settings, with a light final polishing or burnishing.

3 6.2 Because it is necessary to work platinum settings with considerable firmness, it is also advisable to mount the piece being set in a very firm anvil/setting ball vice. Wax and shellac are both used as the bedding material with wax being marginally the more resilient. Warm methylated spirits will remove residues of either without having to disturb the potentially good prepolished finish of the setting. A final detailed polish may be applied with green rouge (chromic oxide), rather than crocus, because it drags less. piece. When working on a group of stones, the close setting possible with platinum dictates that you work from the centre progressively outwards. Claws are levered first against the centre stone until they are all spaced evenly around the girdle, using the surrounding material as the "purchase" for twisting/levering the setting tool. The process is then repeated on the next outer position and so on. This is particularly important with pavé settings (no prongs) in order not to run out of beadable material around the centre stone. Claw Settings (Figure 6A.) The ability for platinum to provide strong slender claws, for setting diamonds safely but with maximum exposure, is sufficiently well known not to need elaboration here. Figure 6B. Claw settings. Pavé Figure 6A. The claw setting is the earliest and best known application of platinum in jewellery. Claws can be light in section provided there are distinct notches near the claw end to locate the pavillion below the girdle; the "Radial Tightness" of platinum claws is sufficient. A typical traditional but high and open presentation of a solitaire diamond. Platinum has been used successfully in all of the classical claw type settings for single stone rings, two to five stone straight or waveform settings with scallop, arcade, scroll, organ-pipe styles or decorations. It is certainly not limited to setting diamonds. The common feature to most claw settings using platinum is that stones can be supported on thinner bezels, narrower bearers and with fewer slender claws than with most other hall-markable precious metal alloys. Most users of platinum prefer to start with material as near to finished shape and size as possible, to minimise the amount of platinum scrap. This immediately emphasizes the advantage of precision casting the settings or even the whole An important application of platinum is in making the settings for pavé work (setting diamonds or other small stones close together, similar to cobblestones). In some respects this may be viewed as a development of the classical cluster setting whereby a group of stones, not necessarily all the same size, are set in a shallow domed circle. In pavé work, (Figure 6C) a small plate, shallow dome or even a hemisphere of platinum can be drilled out until the holes are almost touching, but there can still be enough Figure 6C. Pavé setting. (A) A typical hole drilling plan for a close-packed hexagonal arrangement for 5-10 point diamonds; (B) All holes are first drilled parallel sided; (C) Top bearers are then made by countersinking; (D) Similar opening out of the pavillion; (E) Adjacent almost radial cuts provide a tongue to form a bead over the edge of the girdle which is cleaned up with a grain tool; (F) Each stone is held by three beads.

4 6.3 strong metal remaining in the network to retain closely set stones at their girdles and show little more than the raised bead. In this case, fully annealed material should be used to avoid the difficulty of hard spots in unannealed alloy making the raising of beads or close fine setting difficult, thus outweighing the advantage of increased metal strength. Of course there is no point in reducing the thickness of the platinum to such an extent that the culets of the stones make uncomfortable contact with the wearer. Normally the pavé platform is raised on the ring shank or brooch surround with a gallery or basket back similar to those used for cluster rings. Pavé and similar close display settings are normally prepared by drilling recesses in small sections of sheet or cleaning up recesses in precision cast components and then producing an accurate seating with a precision burr or fraise. As with any other setting material, it is important to match the stones beforehand so that it is not necessary to produce too much variation in seating sizes with the burrs. Only in mass production is wear of drills and burrs likely to be a problem. Figure 6E. Channel settings. (A) to (c) handmade channel ring for square or baguette stones with inside edges cut to form bearers from two flat rings and with spacers which must clear the stones so they lie end to end (d) to (e) shows cast channel section with (f) cast-in bearing which needs finishing with an onglette graver (use flatter 15 cutting edge than normal for gold at 30 to 40 ) to seat the girdle just below the rim of the channel (F), before turning the edge back over the stones (h) with a setting tool. touching girdles. Cast channels may not need many, if any, cross-spacers and the beginnings of the bearer recess may be cast into the inner upper edge of a standard channel. This reduces the amount of graver work needed to complete the bearer and of course reduces the weight of the ring (Figure 6E). The bearer is deepened sideways into the channel edge with an onglette graver, the baguettes are 'snapped' in and the thin top edge of the channel is forced over just above the girdle of the stone. Figure 6F. Channel settings. Figure 6D. Pavé setting. Channel Setting Platinum is very good for making channel settings for much the same reason as pavé; baguette stones can be adequately supported by strong but narrow edge bands, leaving the end girdles of the stones touching apparently unsupported in the centre of the channel. In practice, the sides of the channel will be cross-braced with spacers, particularly if handmade, but platinum does not normally need cross-spacers below every pair of Invisible Setting Platinum readily supports the principle of pavé and channel settings in that the continuity of the stones from one to another is emphasized without drawing too much attention to the setting itself because it is strong but slender. It is possible to arrange the stones in such a way that no platinum is visible between them (Figure 6G). This is done by cutting special grooves or inset slots in the gemstones just below the girdle. These receive very carefully prepared claws which allow the stones to touch at the girdles above. Either the crown facets, or total internal reflection

5 6.4 Figure 6G. Principles of invisible settings. (A) to (C): Triangular, square/rectangular, hexagonal stones are best for close packing: (D) Six-rayed star-cut stone in plan and elevation; (E) Double French or Cardinal cut similarly showing the position of hidden grooves in all or alternate facets below the girdle into which pre-set prongs spring to hold the pattern in place. in the case of diamonds and some simulants, hide from view the small penetration into the pavillion. This type of arrangement obviously depends on strong claws with some springiness and they must still be small to be well hidden. Platinum is ideal for this application. stresses some gemstones will safely withstand, it is possible to support the stones more openly than would be possible using conventional settings. In effect the stone is clipped in a gap cut into a prestressed ring of platinum. The gap is slightly less than the diameter across the girdle of the stone and when clipped into simple curved notch seatings in the open ends of the ring, the stone is held firmly by elastic hoop stress. The stone appears to be suspended in space (Figure 6I). A similar principle may be used to hold the stone in a "split tube" setting. Figure 6I. A tension ring setting. Figure 6H. Invisible settings. Unusual Settings The high mechanical properties of platinum and the fact that it does not soften or relax with time (except at high temperatures) has led to its use in some innovative types of settings. The basis of most of these is that the stress created by elastically deforming platinum is predictable and can be relied upon to grip a stone without relaxation. By combining engineering stress calculations with a good knowledge of what Figure 6J. Tension settings.

6 6.5 Setting and Mounting Techniques It is good practice with platinum to: Drill at a slow speed. Start holes with a pilot drill and then use a drill size smaller than the stone to finish. Use sharp drills, resharpening often. Lubricate with beeswax or methyl salicylate (oil of wintergreen) frequently. If the drill breaks, dissolve out with 30% sulphuric acid. Use a new or well-cleaned burr only as much as necessary to finish the seating. Keep millgrain wheels and burnishers meticulously clean and reserved only for platinum. Opinions differ as to the best tools for setting platinum against stones. It helps to have a matt texture, to get an accurate positioning without slipping in the initial stages of moving platinum onto the girdle of the stone. On the other hand, the finishing of the beading and the tidying up of the surrounding setting is best done with a highly polished burnisher. Platinum burnishes well, but it also drags easily in contact with the slightest trace of debris. Transfer of debris from tools is avoided by repeated retouching of the high polish on the tool face after every few strokes. This is not as arduous as it sounds if the initial polish on the tool face is good. While a 4/0's emery finish is good enough on a burnisher for gold, it is advisable to use something better for platinum. One classical method is to use putty powder mixed with methylated spirits, spread on a smooth piece of hardwood as the touch-up polisher. Methyl salicylate (oil of wintergreen) in a piece of sponge also acts as a good quick lubricant for the next series of strokes after each tool repolishing. For only occasional use, hardened tool steel scorpers may be used for platinum setting, provided the working face is highly polished, though tungsten carbide tools take and retain the best polish and should therefore be used for repeated work on platinum settings. In particular, the cutting edge of a tungsten carbide scorper gives the sharpest and neatest cut. Setter's Wrist! Advice on firmness of support, sharpness of tools, lubrication, leverage, and as-cast setting surfaces, is given in the interests of good quality platinum settings, but there is another aspect. The occasional worker in platinum often complains that "platinum is hard on the wrists"! Typical platinum settings do offer more resistance than, say, 18 carat yellow gold, but this is the reason for its success as an apparently slender but strong setting for the stones. There is usually no need to "move" as much platinum about in cutting a seating, making a bead over a girdle, or setting a claw, as would be the case with softer alloys. Use short cutting strokes and frequent lubrication; lever claws and material for beads into place and maintain all tools in top condition. Above all, cultivate a policy of "right first time", with careful preplanning of each part of the setting operation. Much of the frustration with platinum comes from having to rework your, or someone elses, previous errors, usually on now work-hardened material, and having to remove defects in otherwise well-polished areas!