Quick start
Drop a design file on the home page, or load one from the Design Library. Every panel fills in automatically: design data, 2D views, the cutting chart, the 3D preview, and the light-return analysis. Nothing changes your original file; edits live in a working copy until you export.
Loading designs
- .gcs — Gem Cut Studio files.
- .gem / .asc — GemCAD files, both ASCII cutting instructions and the binary .gem library files from FacetDiagrams.
- Create Chart Manually — build a cutting chart from scratch (with its own preview and analysis).
- Design Library — designs you save with "Save to Library" are stored in this browser, with a thumbnail and search. They never leave your computer.
- Copy Share Link — puts the whole cutting chart into a link; opening it rebuilds the design.
- Recent designs — the last five designs you loaded appear on the home page; click one to rebuild it. Stored in this browser only.
Design Information
Facet and tier counts by section, and the standard proportions relative to the stone's width W: L/W (length), T/W (table), P/W (pavilion depth), C/W (crown height), H/W (total height), U/W (culet), V/W³ (volume), P/C (pavilion-to-crown). "Angles for R.I." is the material the angles were designed for; the critical angle comes from it. Enter a Width (mm) under Size Data to see the proportions in real millimeters plus an estimated carat weight (density comes from the design's material; override it in the Density box). The width is shared with the export dialogs' Size field and prints on the cutting sheet.
The meet points line checks the solved geometry. Green: every meet closes. Gray: small near-misses at or below cutting precision (under ~0.5% of width) — common in binary .gem imports and after tangent-ratio or gear conversions, and nothing to worry about. Orange: gaps a 10x loupe can see; click the line to mark the spots on the 3D preview. Not every design is a meet-point design, so deliberate non-meets can flag too — the line matters most when a design that was clean flags AFTER you edit it. If the notes are just noise for your designs, click hide to fold the line to a small chip; the choice is remembered, and a show link brings it back. Exports still include the full verdict.
2D Preview
Orthographic outlines: Crown (looking down), Pavilion (looking up), Side, and End profiles. These match the diagrams printed on cutting sheets.
Cutting Charts
- Angles are cutting (protractor) angles. Red marks a pavilion angle below the critical angle (it will window); amber means within 2 degrees of it.
- Click an angle or index cell to edit it. The design re-solves immediately, the EDITED banner appears, and "Revert to original" undoes everything. Ctrl+Z steps back one edit at a time; Ctrl+Y (or Ctrl+Shift+Z) steps forward again.
- Index Rotation renumbers the indices without changing geometry. Hand Shaped replaces girdle rows on the printed chart.
- Tangent Ratio retargets all angles for a different material while preserving the stone's outline.
- Convert Gear moves the design to a different index gear and is honest about rounding: non-exact notches are flagged with the cheat in degrees.
- Bench Mode — a full-screen at-the-machine checklist: tiers in cutting order with large angles, a done checkbox per tier, and personal cheater notes (saved in this browser only, never exported with the design).
Design Builder
Author a design from scratch ("Start from Rough" on the start page) or restructure a loaded one ("Edit in Builder" above the cutting chart). The builder edits an ordered cut list; every change re-solves the real geometry, so all previews, the ISO analysis, and every export stay live.
- Index wheel — a plain click SETS the selected tier's indexes to the clicked symmetric set, so clicking around moves the whole set; Ctrl+click adds a second set, clicking a selected notch removes its set, and turning Assist off toggles single notches. The lines under the wheel show the tier's current index numbers and, while you hover, a live preview of exactly which numbers a click would select. Tier symmetry sets how many rotational copies (plus mirrors) one click places — per tier, seeded from the design.
- Live preview — the builder's own 3D view (drag to rotate, scroll to zoom) highlights the tier being edited; dragging the depth slider or nudging an angle shows the actual cutting planes moving, with the solved stone following right behind. Dashes on the wheel point where the facets appear in the matching 2D plan view (crown tiers use the crown view's orientation, pavilion tiers the pavilion view's); other tiers of the same section show as faint inner dashes. Fractional indexes from loaded fancy cuts draw at their exact angles and are never rounded.
- Depth modes — Auto meet cuts the tier until it lands on the meet points made by earlier tiers (the girdle line for a section's first tier). Fixed gives you a slider for broad strokes plus fine (‹ 0.001) and coarse (« 0.01) arrows and a directly editable number — step cuts' inner depths and the overall depth are design choices meets can't decide for you. Table size cuts the flat crown facet to a target T/W. Everything updates the stone continuously while you drag, and the cutting plane rides the facet being adjusted in the builder's 3D view.
- Cut to meet point — select a tier, press the button, then click one of the marked meet points in the builder's 3D preview: the tier's plane is cut exactly through that point (the classic way to land the table on a chosen meet). Rotate the preview to reach points on the far side. Click any facet in the preview (outside pick mode) to jump to its tier in the cut list; while pick mode is armed, middle-click does the same.
- Girdle & outline — a single symmetric girdle's distance is just the stone's overall scale (adjusting it changes nothing visible — every ratio stays the same), so the builder shows "outline scale" there instead of a dead knob. The outline is shaped by the L/W control (girdle tiers in Outline mode, when ends and sides are separate tiers) or by giving multiple girdle tiers different fixed distances. Girdle U/W sets the girdle thickness that auto-meet crown tiers are cut against. Long axis picks which index pair L/W stretches (96–48 by default) — swap it if your design's ends and sides are the other way around.
- Re-meet — on a loaded design, depths stay exactly as the file had them until you say otherwise; Re-meet re-derives the selected tier's depth (or all of them, in cutting order) by cut-to-meet.
- Cutting order matters for auto depths: a tier meets the tier ABOVE it in its section's list. Reorder with the arrows, or duplicate a tier (same indexes, 2° shallower, auto meet — the step-cut shortcut). The cut list is grouped into Pavilion and Crown — click a group header to fold that half away (a collapsed group still shows a status dot if one of its tiers has a problem). Pavilion angles turn red when below the critical angle for the design's R.I. (they will window) and amber within 2° of it.
- Typed charts — a chart entered in "Create Manually" can be turned into real geometry: press Solve in Builder there. Every depth is derived by cut-to-meet (the chart needs a 90° girdle tier), and the design opens here with full analysis and export.
- An amber status dot means the tier's facets were eliminated by later cuts or kept a stale depth — adjust its depth (or angle) until it turns green.
- The chart below the builder shows the solved result and is read-only while the builder is open; undo (Ctrl+Z), the EDITED banner, and Revert work as for any other edit.
- Show step in main 3D sequence drives the main 3D panel's cutting-sequence view to the selected tier, showing the (cube) rough cut up to that point.
3D Preview & Ray Traced
- Drag to rotate, scroll to zoom, or use the Snap buttons (Crown, Side, End, Pavilion, Oblique). Render modes range from wireframe to per-tier coloring to the full Ray Traced mode. In Ray Traced mode the initial view is the maximum zoom; scrolling shrinks the stone and brings it back.
- Ray Traced: pick a material preset (each carries a realistic absorption curve) or use the color picker; adjust IOR, dispersion, absorption, haze, and bounces.
- Lighting setups simulate a room, studio, daylight, tungsten, or the ISO sky used by the analyzer; the Key sliders move the main light. The beauty presets flatter stones: Diamond Photo is a bright light box whose dark observer zone draws the black arrows pattern, with tiny hot sparks sized at the dispersion angle so fire actually colors; Spotlights and Sunlight are moodier small-light setups; Studio HDRI loads a real photographed environment (bundled, ~6 MB) on first use. Small-light presets look their best in Render HQ — the interactive view samples one exit per pixel and understates tiny sources; judge them with the HQ dialog's draft preview.
- The Pattern backdrop (checker/grid) is a windowing test: a windowed stone shows the pattern straight through its table, like reading newsprint through the pavilion.
- Save PNG downloads the current view. Render HQ makes a high-quality still of it: pick a resolution (up to 4096px) and pass count, watch the preview converge live (sub-pixel accumulation cleans the edges, spectral accumulation melts dispersion into continuous fire), then save the PNG. Cancel keeps the partial image. The dialog's Lighting select switches presets with an instant low-quality draft preview, so you can audition setups before committing; the environment detail is also rendered at higher resolution for HQ output (the 512-pixel interactive env cube is what read as soft at 4K). Path-traced physics (on by default) additionally follows the interior partial reflections the realtime shader discards — the secondary scintillation of a real stone — and traces each sample at its own wavelength, so fire emerges from genuine path differences; the preview starts grainy and converges with the passes. Accumulation happens in linear light on GPU float buffers with the tonemap applied once to the converged result, so the HDR lighting's bright flashes keep their true energy instead of being clamped pass by pass. Expect roughly half a minute to a few minutes depending on settings and GPU. Reset reseeds the material from the loaded file.
- Show Cutting Sequence steps through the design tier by tier or facet by facet.
ISO Brightness
- The headline percentage is GemRay-style face-up light return: the lit fraction of the view from directly above under a uniform sky, with your head shadowing the center cone.
- The heat map shows where that light comes back: bright cells return light, dark cells are windows or extinction.
- Analyze at R.I. answers "what if I cut this in a different material" without changing any angles; the comparison renders side by side (solid = design, dashed = what-if on the tilt chart).
- The tilt sweep rocks the stone ±30°. "Tilt directions" above 1 tips it over several axes and shades the band between the best and worst direction.
- Optimize Pavilion / Optimize Crown sweep that section's angle (the rest held fixed) and pick the brightest setting whose windowing is no worse than your current design. "Convert design" applies it through the normal edit pipeline, so Revert always works.
Reading the graphs
The brightness graphs all share four metrics. On the tilt charts you choose which to show (checkboxes in the editor, a menu in Compare and the optimizer):
- ISO Brightness — the headline face-up light return. Light is sampled straight down onto the stone; this is the share that bounces back out toward the sky. Every returning ray counts equally. Higher is brighter face-up.
- COS Brightness — the same returning light, but each ray weighted by how steeply it leaves the stone. Light coming straight back up toward your eye counts fully; light leaving at a shallow, glancing angle counts less. It sits a little below ISO and tracks how much brightness actually aims at the viewer instead of spilling off to the side.
- Window — the share of light that passes straight through and leaks out the back instead of returning. This is literal see-through: a high or rising Window means a stone you could read newsprint through. This is the one you want low.
- Table Brightness — ISO brightness counting only the rays that enter through the table (the big top facet). It isolates how bright the central zone your eye lands on first is, ignoring the crown facets around it.
Brightness vs tilt rocks the stone ±30° and plots the chosen metric at each tilt, so you see how brightness holds up (or windows out) as the stone moves, not only dead face-up:
- Editor chart: each checkbox turns one metric's colored line on or off (slate = ISO, gold = COS, orange = Window, purple = Table). A solid line is the design; a dashed line of the same color is the "Analyze at R.I." what-if overlay.
- Optimizer chart: slate = your original angle, green = the adjusted angle, both solid so the curve shapes compare honestly.
- Compare chart: the menu picks one metric; slate = design A, green = design B. With more than one tilt direction, a faint band shows the spread between the best and worst direction.
- The summary line under the chart reports avg ±15° (mean brightness over a realistic hand-rock), retention (that average divided by the dead-face-up value), and where windowing first appears. Retention above 100% is normal and good: it means the stone is brighter rocked slightly off-axis than at dead center, where your own head shadows the middle. It is not an error or a bug.
Optimize Pavilion / Optimize Crown charts sweep that one section's angle with the rest of the stone held fixed, and plot at each angle:
- Dark line = ISO brightness, purple = Table brightness, orange = Window (the same four metrics above).
- Red dashed = the critical angle (pavilion only): below it the pavilion stops reflecting and windows.
- Gray dashed = the design's current angle.
- Green ring / dashed = the chosen angle: the shallowest angle whose brightness is within 1% of the peak and whose windowing is no worse than your current design. The slider lets you explore any angle and read its numbers before converting.
Compare Designs
Put two designs side by side with one set of controls: rotation, snaps, render mode, and lighting drive both previews together (drag either canvas), and one Analyze runs both ISO analyses. The tilt chart overlays both designs as solid lines, A in slate and B in green; the "?" on the chart explains every metric.
- Start from the home page ("Compare Two Designs", pick two files), from the editor ("Compare With…"), or by clicking Compare on two library cards.
- In Ray Traced mode each stone renders with its own R.I. and color. "Analyze both at R.I." puts both on the same material for the brightness comparison.
- Compare is read-only; use "Open in editor" under either design to work on it.
Exporting
- Export Full Design — the comprehensive PDF: data tables, meet-point check, all four diagrams, ray-traced previews, any edit/conversion note, the cutting chart, and the light analysis.
- Export Cutting Sheet — a bench-ready PDF; the dialog controls sections, diagrams, print size, and paper. A Width (mm) set under Size Data prints in the header with the estimated carat weight.
- Export GCS / GemCAD — design files. An unedited .gcs exports as the exact original bytes; edited designs export regenerated files with an "_edited" suffix.
Good to know
- Your view and analysis settings (lighting, pattern, ray counts) are remembered by this browser.
- The app asks before a reload or a new design load would discard unsaved edits, notes, or an open builder cut list; "Save to Library" keeps a copy first.
- Everything runs locally; no design data is uploaded anywhere.
- Most controls have tooltips: hover over a slider or option for the details.
- The small "build" stamp at the bottom of the Ray Traced View column tells you which version of the app the page is running.