DDG Ass #13 Grading Pavilion and Finish PDF

DDE -Ass #13 - Grading Proportions - Pavilion & Culet & Finish The Pavilion: - A diamond’s pavilion facets take the light that enters from above and reflect it back toward the crown, giving the diamond its spectacular brightness & unique ability to break up light into its spectral colors and create...

DDE -Ass #13 - Grading Proportions - Pavilion & Culet & Finish The Pavilion: - A diamond’s pavilion facets take the light that enters from above and reflect it back toward the crown, giving the diamond its spectacular brightness & unique ability to break up light into its spectral colors and create fire. - The pavilion depth percentage is the distance from the bottom of the girdle plane to the culet, expressed as a percentage of the average girdle diameter The pavilion angle is the angle formed where the pavilion mains meet the girdle plane. Estimated the Pavilion Depth Percentage -estimation is usually accurate enough for grading and appraising and is process that simply involves identifying and interpreting the reflections seen through a diamond’s table. - Minor cutting variations, like misalignment between the crown and pavilion, or even a slightly tilted facet, change the reflection pattern of the star facets. Even if they form only a partial outline of the table reflection, they still help you locate it. - For Example: If the table reflection reaches about halfway from the culet to the table corner, the pavilion depth percentage is 44.5 percent. -Generally, the greater the pavilion depth percentage, the steeper the pavilion angle -Steep pavilion angles produce dark areas under the diamond’s table. Shallow pavilion angles, in combination with large tables and shallow crown angles, might produce unattractive reflection effects like fisheyes. The Girdle Lower, Half Facets and Culet - The final information needed to determine a diamond’s cut grade are girdle thickness percentage, lower half length percentage, and culet size. - Girdle thickness percentage is the thickness of the diamond’s girdle expressed as a percentage of its average girdle diameter. -Lower half length percentage is the length of the lower half facets expressed as a percentage of the total distance between the girdle and the culet. - The Culet size is the size of the facet at the bottom of the diamond where the pavilion mains meet. Girdle Thickness Percentage: - This parameter is assessed at the girdle’s thickest areas—the hills—where the bezel facets meet the pavilion main facets -Girdle thickness percentage can limit a diamond’s possible cut grade. Girdle Thickness Percentage = Total Depth % – Crown Height % – Pavilion Depth % (Round the result to the nearest 0.5 percen) Lower Half Facets Percentage: -Lower half facets start at the girdle and extend toward the culet - To establish an estimate examine all eight pairs of lower half facets as you move clockwise around the gem. Consider the distance between the culet and the girdle as 100 percent. Estimate the distance each lower half facet reaches toward the culet. Culet Size: -Its purpose is to prevent abrasion and chipping on loose diamond - To establish and esitmate examine the stone face-up at 10x magnification under darkfield lighting to view th culet area, rocking back and forth to see if there is a blink indicating the diamond has a culet -The size of a diamond’s culet limits its possible cut grade. - If the pavilion comes to a sharp, unabraded and undamaged point, the culet might be described as “pointed.” -When the culet is at more than a slight angle to the table facet, consider it an extra facet rather than a culet and report culet size as “none.” -Include the presence of any clarity characteristics in your assessment. When there’s a chip, cavity, or indented natural at the culet, consider only the remaining portion of the culet facet under culet size, and judge the clarity characteristic in the diamond’s clarity grade. - the presence of a culet should reduce your estimate of pavilion depth percentage. Total Depth Percentage: - You can calculate total depth percentage by adding crown height percentage, girdle thickness percentage, and pavilion depth percentage estimates together. Total Depth Percentage = Crown Height Percentage + Girdle Thickness Percentage + Pavilion Depth Percentage Design and Craftsmanship: -Design is determined during the fashioning stage. It’s a diamond’s physical shape, including its proportions, durability, and weight -Craftsmanship is the care that goes into the diamond’s finishing details. -Ratings for polish and symmetry are included in this category. -Including these factors gives a well-crafted diamond the recognition it deserves and properly identifies the factors that make it more beautiful than other diamonds. Relating Weight to Proportions: -GIA Cut Grading System is a determination of the diamond’s weight in relation to its diameter when compared to a reference diamond with a similar average girdle diameter and standard proportions. Graders call this “weight ratio.” -If a diamond’s total depth percentage is more than 65 percent, it’s an indication that its crown, pavilion, or girdle— or all three—are too thick. -Hidden weight in extra-thick girdles, steep crowns, or deep pavilions are features that make a diamond heavier than their millimeter diameters suggest. They represent poor value because a customer pays for extra weight that doesn’t show in the diamond’s face-up appearance. Finish: Finish is made up of two subcategories: polish and symmetry. Polish is the overall condition of a finished diamond’s facet surfaces. Symmetry refers to the exactness of the shape and the placement of its facets. Polish and symmetry assessments are based on the degree of visibility of all the diamond’s variations in face-up and profile views under 10x magnification. Polish: A diamond must be well polished to produce sharp reflections and undistorted light transmission. Poor polish makes stones with even the best proportions look dull and hazy. Polish characteristics can be a result of the finishing process or be affected by blemishes created after cutting. To evaluate polish, examine the diamond under 10x magnification and look for blemishes that might affect polish., Such as: Abrasion, Lizard Skin, Nick, Pit, Polish Lines, Rough Girdle, Scratch, Burn, Polish Mark, Laser Manufacturing Remnant Abrasion (Abr): A series of minute scratches or pits along a facet junction, giving the edges a white or fuzzy appearance. Lizard skin (LS): Wavy or bumpy area with a transparent, pitted texture, which results from polishing off-grain near a cleavage plane. Nick (Nck): A small notch on a facet junction with no readily apparent depth at 10x, usually along the girdle edge or culet. Pit (Pit): A small opening that looks like a tiny white dot at 10x. Polish lines (PL): Fine, parallel grooves and ridges left by the polishing process. Can appear white (Wht) or transparent (TP), heavy or light. Heavy polish lines leading from a surface feature, such as a cavity, are called drag lines. Rough girdle (RG): Irregular or granular surface of a bruted girdle, consisting of pits and nicks. Scratch (Scr): A thin, dull, white line across the diamond’s surface, with no apparent depth. Burn (Brn): Whitish haze across a facet, caused by excessive heat during polishing or, rarely, by fire from a jeweler’s torch or other source. A surface burn resulting from excessive heat where the dop touches the diamond is called a dop burn (Dop). Polish mark: A surface feature that resembles an extra facet without a distinct or straight facet junction. Laser manufacturing remnant (LMR): Remains of laser cutting or marking left on the surface of a polished diamond. Affects polish when it’s confined to the surface when viewed at 10x. Symmetry : -Facet diagrams of round brilliants show a precise arrangement of 58 perfectly shaped facets. -Most diamonds have at least a few symmetry variations, but they typically have little effect on appearance, at least to the unaided eye. -Compare the sections against each other. All eight sections should match. If they don’t, the diamond isn’t symmetrical. -Most symmetry variations are proportion-related and have to do with the alignment and balance of the stone’s table, culet, girdle, and angles. -Other symmetry variations relate to the shape, placement, and presence or absence of the facets themselves. -Examples are: Out of Round, Table Off Center, Culet Off Center, Table Culet Alignment, etc -A diamond with variations in alignment probably also has misshapen facets and pointing. These three variations almost always occur together. When you notice one, check for the other two. Out-of-round (OR): The girdle outline doesn’t look perfectly round. Might also have a flattened area, referred to as an uneven outline. Table off-center (T/oc): The table is not centered in the crown. If a bezel on one side of the crown is longer than the bezel on the opposite side, this indicates that the table is off-center. Culet off-center (C/oc): The culet is not centered in the pavilion. If you see more of the pavilion on one side of the culet, this indicates an off-center culet. If the cross-line formed by the pavilion facet junctions appears bowed or bent, this indicates an off-center culet. Table/culet alignment (T/C): Table and culet are displaced in opposite directions. Girdle thickness variation (GTV): Variations in girdle thickness that, on a brilliant cut, might occur in the areas where crown and pavilion facets meet. Crown angle variation (CV): Variation in measurements of all eight crown angles on a round brilliant. Typically related to T/oc. Pavilion angle variation (PV): Variation in measurements of all eight pavilion angles on a round brilliant. Typically related to C/oc. Crown height variation (CHV): Variation in the diamond’s eight crown height measurements. Pavilion depth variation (PDV): Variation in the diamond’s eight pavilion depth measurements. Star angle variation (SV): Unequal star facet angles. Star percentage variation (SPV): Variation in the diamond’s eight measured star facet length percentages. Upper half variation (UHV): Unequal upper half facet angles. Lower half percentage variation (LPV): Variation in the diamond’s eight measured lower half facet length percentages. Lower half variation (LHV): Unequal lower half facet angles. Missing facet (MF): A facet that should be in a given location is absent. Extra facets (EF): Facets not required by the cutting style are placed without regard for the diamond’s symmetry, most often near the girdle. Natural (N): A portion of the original surface, or skin, of a rough diamond left on a fashioned stone. Non-octagonal table (T/oct): The table doesn’t have eight sides of equal length and parallel opposing sides. This results in star and bezel facets that are also misshapen. Misshapen facets (Fac): Facets are not properly shaped, or they’re not the same size and shape as others of the same type. On a brilliant cut, misshapen facets might be described more specifically as misshapen bezel (MB), misshapen star (MS), or misshapen main (MM). Non-pointing (Ptg): Facets fail to meet at precise points, or a fully formed facet doesn’t reach its prescribed location. On a brilliant cut, Ptg might be described more specifically as open main (OM), open bezel (OB), short main (SM), or short bezel (SB). Misalignment (Aln): Crown and pavilion facets not aligned with each other. Either the points of the bezel and main facets do not align across the girdle, or the facet junctions of the upper and lower half facets do not align. This might be referred to as “twist” in the trade. Rating Polish ans Symmetry: - graders rank the stone’s polish and symmetry separately under the “Finish” heading. For each category, they use the ratings Excellent (Ex), Very Good (VG), Good (G), Fair (F), and Poor (P). - If polish or symmetry—or both—are rated Excellent, that means they’re “superior.” - It doesn’t mean “perfect,” so a diamond with just a few very hard-to-find polish lines or some very slightly misshapen facets could still get an Excellent rating. - only faint polish lines or insignificant blemishes, and very slight misalignment between the crown and pavilion, its polish and symmetry are Very Good. - Good rating if it has transparent polish lines on the crown that are visible through the pavilion, several small blemishes, a table or culet very slightly off-center, several extra facets, or noticeable misalignment between the crown and pavilion. - Obvious polish lines, burn, noticeable blemishes, a wavy girdle, a number of misshapen facets, or noticeable pointing warrant a rating of Fair. - Poor rating usually has either polish characteristics that reduce transparency or obvious symmetry variations. Putting it All Together: -Each of these factors to consider are: Carat weight compared to average girdle diameter, Total depth percentage, Table percentage Star length percentage,Crown angle, Crown height percentage, Girdle thickness,Girdle thickness variations Pavilion depth percentage, Pavilion angle, Girdle thickness percentage, Lower half length percentage Culet size, Polish and symmetry -Each factor limits the diamond’s potential cut grade, and the one that rates the lowest determines the grade. -The proportion factors that play the biggest role in determining a round brilliant diamond’s brightness are table percentage, crown angle, and pavilion angle. -Even though the lowest parameter often sets the cut grade, two or more factors might interact negatively to reduce the cut grade below what you might expect. -It’s important to place more emphasis on the way a diamond actually looks than on its numerical parameters.