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

  • 2022 USFG SSC Novice Design – Changes for Corundum

    Posted by lauralindberg on December 27, 2021 at 5:05 pm

    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?


    • This discussion was modified 2 years, 6 months ago by  lauralindberg.
    Alan Balmer replied 2 years, 6 months ago 5 Members · 6 Replies
  • 6 Replies
  • scottwkelley

    December 27, 2021 at 10:20 pm

    It will look fine at those angles.

  • ozgurertan

    December 28, 2021 at 4:18 am

    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.

  • lauralindberg

    December 28, 2021 at 12:01 pm

    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.

  • Alan Balmer

    December 28, 2021 at 12:10 pm

    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 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.

    Gemstone Design Conversion Using the Tangent Ratio Method

  • raakeshnambidiveetil

    December 29, 2021 at 8:25 am

    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.

  • Alan Balmer

    December 29, 2021 at 12:57 pm

    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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