DDG Ass #15 Estimating Weight, Recutting, and Repolishing PDF

DDG Ass #15 Estimating Weight, Recutting, and Repolishing Grading Mounted Diamonds: -A mounting almost always makes it difficult to assess a diamond. It’s impossible to accurately weigh a mounted diamond, and the mounting can cover some parts of a stone and make measuring a challenge. -It can also...

DDG Ass #15 Estimating Weight, Recutting, and Repolishing Grading Mounted Diamonds: -A mounting almost always makes it difficult to assess a diamond. It’s impossible to accurately weigh a mounted diamond, and the mounting can cover some parts of a stone and make measuring a challenge. -It can also hide a diamond’s imperfections and affect its apparent color. Evaluating Clarity: - A fiber-optic lighting system can help, because the light’s brightness and focus are adjustable and the lamp’s flexible pipe allows the light to be directed where it’s needed. - Prongs often hide blemishes and inclusions. You can see what’s under a prong by finding the prong’s reflection in the opposite side of the pavilion and carefully examining the area around it. -With higher-clarity diamonds, you might have to remove the diamond from the mounting to obtain accurate grading results. -appraisers usually state a single clarity grade for large diamonds and a range of two possible grades for small ones, also state that the diamonds are mounted Evaluating Color: - Use one of these observation methods for diamonds in the D-to-Z color range: If the diamond is in a solitaire setting, holding the mounting so the diamond is in the table-down position as you move it along the row of masters. Another method is to hold the masterstone in tweezers, with its table close to the table of the mounted diamond and compare corresponding crowns If the crown is not visible in the profile view, another option is to hold the diamond and the masterstone side by side to perform a face-up color comparison. - The metal can also influence the diamond’s apparent color. - Large stones are assigned a single color grade, but the small mounted stones generally those under 0.20 ct a range of two possible color grades Evaluating Measurements and Cut: - The mounting might allow you to measure the stone’s dimensions with a millimeter gauge. However, if the mounting covers the girdle edge, you’ll have to estimate the stone’s diameter or length and width. - When a bezel or channel setting hides the edge of the girdle, you have to estimate its location by following the edges of opposing bezel facets down to the rim of the setting and estimating where they would come to a point under the metal then measure from those points - Estimating the crown angle of a mounted diamond is probably easier with the face-up method than with the profile method. - For round brilliants, use the estimated crown angle and table percentage to find the crown height percentage on the Estimated Crown Height Percentage chart in this assignment. - When a bezel setting conceals the girdle, assess the girdle’s thickness and condition by checking its reflection in the pavilion. - On Round Brilliants be sure to judge the thickness between the upper and lower half facets rather than between the bezel facets and pavilion mains. - judge the girdle’s thickness and condition by observing the visible areas, and then assessing the areas hidden by the prongs - Judging the pavilion depths and pavilion angles of rounds is the same for loose and mounted stones. - you might be able to visually judge pavilion depth and pavilion bulge if the mounting allows you to see the stone’s profile - You can determine total depth percentage if you can get the measuring device to contact the diamond’s culet - Judge culet size by looking through the table, just as for loose diamonds. - Judge polish and symmetry as you would on a loose stone, but use reflections to see areas hidden by the mounting - calculate mounted stones’ girdle thickness percentages the same as you would for loose stones: by subtracting the crown height percentage and pavilion depth percentage from the total depth percentage. Estimate Diamond Weight: -professionals use mathematical formulas to estimate the weights of mounted round and fancy-cut diamonds. The formulas assume fairly standard, modern proportions and basically symmetrical designs. -the key to accurate weight estimation is experience. Practice with loose stones, first estimating and then weighing to check your results. Adjusting Shape and Proportion Weight Percentage: - A thick girdle adds weight at the widest part of the diamond, so of all the possible proportion variations, girdle thickness has the greatest effect on estimated weight. -To allow for this, use the Weight Correction Factors for Thicker Girdles chart. -These weight corrections apply to round and fancy-shape diamonds with slightly thick or thicker girdles. -Diamonds of all shapes require weight corrections—which range from 1 to 12 percent—for girdle thickness. - Fancy cuts also need weight corrections for girdle outline variations like high shoulders on pear shapes and ovals; bulged wings on pears, hearts, and marquises; or pavilion bulge on emerald cuts. -Depending on how obvious the variations are, select a weight correction factor from 1 to 10 percent. Then Add this to any correction for girdle thickness. Weight Estimation Procedures: - To estimate the weight of a round brilliant, you have to know its average diameter and depth in millimeters and its overall girdle thickness. -If the stone is prong-set, find the average diameter by measuring the girdle diameter in as many places between the prongs as you can. -To estimate the weights of fancy cuts, you have to know length and width. For most fancy cuts, length is the longest dimension and width is the longest of the dimensions that are perpendicular to the length. -If a triangle’s sides are about equal, any side can be the width. If one side is noticeably longer or shorter than the other two, use that one as the width. - On hearts, length is the distance from the point to an imaginary line across the tops of the lobes. -The points on marquises, pears, hearts, and triangles are settings often have V-corners or prongs covering these areas, you have to estimate where the edge is and measure from there. -There’s a figure that’s part of all weight estimation formulas for round brilliants and other shapes -Once you know the length-to-width ratio, use the small charts that assign different adjustment factors to different length-to-width ratios for each shape. - To find the total estimated weight of a cluster of small diamonds(like baguettes or round brilliants) , measure all the stones and, if possible, sort them into size categories. Then figure the total weight of each category and add the category weights together. Repolishing and Recutting: -Repolishing and Recutting have the same purpose: to restore or improve the appearance of a diamond Repolishing: - Repolishing usually involves simply refinishing a diamond to correct minor faults in its clarity or finish. -a cutter might replace some nicks or chips with extra facets. -Some diamonds are judged to be potentials or improvables, Then the lab grades and plots the stone and specifies how its clarity grade might be improved by repolishing. -The clarity of potentials can be raised to Internally Flawless (IF), while improvables can be raised to a VVS1 or VVS2 grade, usually with minor repolishing of surface characteristics. - Three factors determine the effect of a clarity-improving repolish on a diamond’s value: the stone’s color, its old and new clarity grades, and the finished weight. -Polishing or faceting the girdle removes foreign matter and creates a smooth surface. It might also lighten the diamond’s color. Recutting: - Full recutting involves the refashioning of a polished diamond to improve its clarity, proportions, or color, or to modernize an old-style cut. -A damaged round might be recut as a round, or a damaged fancy cut might be recut as a different fancy cut. -A poorly made modern cut might be recut to improve its proportions. Or an old-style cut might be completely recut in a modern style. -A diamond owner rarely sacrifices weight for the sake of beauty alone. The decision is usually a compromise between the two factors, with weight being primary. - When a recut is under considerations the current and expected future appearance and value of the diamond, as well as the cost of recutting it are what is evaluated -Most stones are recut to improve their brightness and their balance between brightness and fire. -When being recut for clarity recutting to eliminate an inclusion can be extremely expensive, but Depending on the nature and depth of the clarity characteristic, laser drilling and bleaching can be a less expensive alternative. -A more common method used to improve a diamond’s color involves recutting to increase rather than diminish color. - But this method often sacrifices 20 to 25 percent of a diamond’s weight and is risk for the cutter who can't guarantee improvement -Diamonds are sometimes recut to update old cutting styles, such as old European and old mine cuts. -However, interest in the older styles is so great that consumer demand now has cutters creating historical cuts directly from rough. Recutting Old Styles: - There are four categories of round or near-round diamonds that can usually be recut effectively into modern brilliants: those with high crowns and deep pavilions, those with shallow crowns and shallow pavilions, those with high crowns and shallow pavilions, and those with shallow crowns and deep pavilions. -Diamonds with high crowns and deep pavilions, like many old-style cuts, can be recut to more modern proportions without much loss in diameter. -Cutters often have to compensate for very shallow rough by cutting shallow crown and pavilion angles and large girdle diameters with large tables, however cutting away such a large portion of the girdle diameter results in significant weight loss, so it’s rarely done. Deciding to Recut Style: -A diamond’s recut style is largely determined by its original cut. -You should know what’s selling and what shapes and colors are rising or falling in popularity. Consulting with a Cutter -Explain the proportions you want, the weight recovery you anticipate, and your expectations, if any, about the clarity grade. Listen to the cutter’s analysis and opinions carefully. -Cutters usually work with angles rather than percentages, so it’s better to explain the pavilion angle you want, rather than the percentage.