Forums Beginner Questions 2022 USFG SSC Novice Design – Changes for Corundum

6 replies, 5 voices Last updated by Alan Balmer 2 years, 4 months ago
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    • #8247

      lauralindberg
      Participant
      @LauraLindberg

      I would like to cut the 2022 Novice USFG competition stone in synthetic corundum and wonder if the pavilion and crown cutting angles should be modified for the higher RI. The design is currently for quartz, a RI of 1.54.

      I believe a person would need GemCad or another software package to determine these angles. I don’t have a software tool available or the knowledge to do this. Has anybody calculated what the P1, P2, C1 and C2 angles should be for corundum (1.76-1.78)???

      Would you loose points for cutting the design in corundum using the quartz angles? Or would it just not be a pretty?

      Thanks!

      • This topic was modified 2 years, 4 months ago by lauralindberg.
    • #8249

      scottwkelley
      Participant
      @scottwkelley

      It will look fine at those angles.

    • #8251

      ozgurertan
      Participant
      @ozgurertan

      As far as the rules concern you are supposed to facet what is given. If the design is for 1.54 the result- the light return- will be better for any higher refractive index so need to change the design or play with it at cad program. İ do not understand People to change the diagrams for higher indexes.

    • #8252

      lauralindberg
      Participant
      @LauraLindberg

      OK I’ll cut as shown, thank you both for getting back to me.

      I was just confused by the instructions “Original angles modified for Quartz” and “Design maybe tangent ratio adjusted to material selected”. I thought that if I didn’t use quartz that something needed to be done.

    • #8253

      Alan Balmer
      Keymaster
      @alanbalmer

      Changing the angles for better performance is allowed, as long as the plan view doesn’t change. The easiest way to do that is using GemCad or Gem Cut Studio, but read https://usfacetersguild.org/gemstone-design-conversion-using-the-tangent-ratio-method/ for an explanation and methods. Bob’s Rock Shop used to have an online calculator, but the site seems to be unavailable now.

      Keep in mind that competition stones are not evaluated for brightness, so it won’t make a difference in your score.

    • #8255

      raakeshnambidiveetil
      Participant
      @RaakeshNambidiveetil

      Hello All,
      Iam a newbie here, I would like to know where to get the details of novice 2022 cutting competation details. Also do we need to come in person to do cutting and submission of stone. Appreciating reply from anyone in the thread please.

    • #8260

      Alan Balmer
      Keymaster
      @alanbalmer

      Are you a USFG member yet? If not, you can join from the link on the home page of this website. All the information will be on this website under the “Competition” menu shortly, and you can download it now from the USFG – United States Faceters Guild page on Facebook.

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