SUNMOONBAY GEM-CUTTING COURSE — STEP 5

Basic Faceting Designs, Angles and Index Settings

Learn how to read a faceting diagram, understand cutting angles, use index settings and position gemstone facets accurately. This beginner's guide introduces the principles behind symmetrical faceted gemstones.

1. What Is a Faceting Design?

A faceting design is a plan showing how a gemstone should be shaped. It typically identifies the facets, their cutting angles, index positions and the order in which they should be cut. Some designs also provide proportions, meet-point information and instructions for transferring the stone between dops.

Following a suitable design helps the cutter produce a gemstone with planned symmetry and proportions. It also helps reduce unnecessary material removal and makes the cutting process easier to repeat.

Different designs suit different rough shapes, gemstone materials and cutting goals. Before starting, check that the design is appropriate for the material and the faceting machine you are using.

2. Understanding the Main Parts of a Faceting Diagram

Facet diagram

A diagram shows the arrangement of facets on the finished gemstone. A top view can show the table and crown pattern, while a side view can illustrate the crown, girdle and pavilion.

Cutting instructions or facet list

Many designs list groups of facets with their corresponding angles and index positions. The order of the rows or groups usually tells you which facets to cut first. Always follow the instructions supplied with the particular design.

Angle values

The angle value indicates the intended orientation of the gemstone relative to the cutting lap or the machine's reference plane. Read the machine manual to understand how its angle scale is defined and calibrated.

Index numbers

The index number identifies a rotational position around the gemstone. It allows the cutter to return to specific positions so facets can be spaced according to the design.

Meet points

Meet points are the junctions where neighbouring facets intersect. Accurate meet points help create an even outline and consistent facet pattern. The required approach depends on the design and cutting sequence.

3. What Are Faceting Angles?

Faceting angles control the orientation of each facet while material is removed. The angle selected for a facet influences where it meets adjacent facets and how the finished gemstone interacts with light.

Pavilion angles

The pavilion is the lower part of the gemstone, beneath the girdle. Pavilion angles are important to the light performance of many transparent faceted designs. If they are unsuitable for the gemstone and design, light may escape through areas that reduce the stone's face-up brightness.

Crown angles

The crown is the upper part of the gemstone, above the girdle. Crown angles work with the table size, pavilion design and other proportions to influence the gem's appearance. The ideal combination varies with the design and optical properties of the material.

Table angle and table facet

The table is usually the largest facet on a standard brilliant-style gemstone. It is normally cut as part of the crown. Its size and alignment affect the face-up appearance, but a table is not present in every gemstone design.

Why you should not guess angles

There is no universal set of angles for all gemstones. Different materials have different refractive indices, and the same material can be cut in many designs. Use a suitable, established design and understand how its instructions relate to your machine.

4. What Is an Index Setting?

An index setting controls the rotational position of the gemstone around its axis. Many faceting machines use an index gear with numbered positions. The selected number corresponds to a particular position around the stone.

For example, a design may require several facets to be spaced evenly around the gemstone. The index instructions help the cutter return to the required positions consistently rather than estimating each position by eye.

Important: Index numbers are not universal instructions by themselves. The same number can represent a different rotational position on a machine with a different index gear. Use the index gear specified by the design or the appropriate conversion instructions.

Index settings help with:

• Repeating facet positions accurately.
• Spacing facets around the gemstone.
• Creating a balanced outline.
• Following a planned cutting sequence.
• Improving repeatability when practising the same design.

5. How to Read a Faceting Instruction

Consider this simplified, fictional example of a facet instruction:

This example illustrates the kinds of information a cutter may encounter. It is not a recommended cutting setting for sapphire or any other gemstone. Actual values must come from the selected design, with the machine and index system properly calibrated.

1. Identify the facet group in the diagram.
2. Confirm that you understand the machine's angle reference.
3. Find the required index position and confirm it is compatible with your gear.
4. Check the design's cutting sequence and intended meet points.
5. Make adjustments only with the machine stopped and according to its manual.
6. Cut gradually, then inspect the facet before proceeding.

6. The Importance of Meet-Point Cutting

Meet-point cutting is a method in which facets are cut to meet at planned junctions. It is widely used for producing symmetrical faceted gemstones.

As each facet is cut, the cutter observes how its edges align with the neighbouring facets. Small corrections may be needed to achieve the intended junctions without removing excessive material.

Tips for better meet points

• Ensure the dop and gemstone are secure.
• Check the angle and index position before each facet group.
• Remove material gradually rather than rushing.
• Inspect the outline and junctions under suitable lighting and magnification.
• Keep a record of corrections so you can identify repeated mistakes.

Do not chase a single imperfect junction by making large adjustments without checking the rest of the design. An adjustment that improves one area may create problems elsewhere.

7. Choosing a Design for Rough Sapphire

Sapphire is a hard gemstone, and its colour, clarity, inclusions, fractures and rough shape all affect cutting decisions. A design should be chosen only after the rough has been examined carefully.

• Colour: Consider how the stone's orientation and design may affect its face-up colour.
• Inclusions and fractures: Avoid designs that would require unsafe or excessive removal around significant defects without expert assessment.
• Rough shape: Choose a design that fits the available material and desired finished outline.
• Optical properties: Use a design suitable for the gemstone's refractive index and intended appearance.
• Potential yield: Balance finished size and weight against colour, clarity, symmetry and durability.

Do not assume that a stone's geographic origin determines its cutting angles. A Ceylon sapphire should be evaluated according to its actual properties and the design being used.

8. Common Faceting Mistakes

Using the wrong index gear

An incompatible index gear can produce incorrect spacing and prevent the facets from meeting as intended. Check the design's requirements before starting.

Misreading the angle scale

Different machines may use different references or adjustment systems. Read the manual and verify that the angle scale is correctly calibrated.

Cutting too quickly

Rushing can remove too much material and make it difficult to correct facet junctions. Work gradually and inspect frequently.

Ignoring the cutting sequence

Changing the sequence without understanding the design can complicate meet-point cutting and affect the final outline. Follow the design's instructions.

Using a design without checking suitability

A design may not suit every rough shape or gemstone. Review the material, optical properties and intended proportions before committing valuable rough.

9. Practice Exercise for Beginners

Use a suitable practice stone and a simple, established design recommended for your machine.

1. Study the diagram and identify the crown, girdle, pavilion and table if present.
2. Locate the angle and index instructions for the first facet group.
3. With the machine switched off, practise identifying the required settings.
4. Check the machine's calibration and the compatibility of the index gear.
5. Follow the instructions with suitable supervision and safety precautions.
6. Inspect the facet junctions and record any corrections needed.

In your notebook, record the gemstone material, design name, machine, index gear, settings, abrasive sequence and final observations. Do not use valuable sapphire rough for your first experiments.

10. Gem-Cutting Safety

• Read and follow the faceting machine and lap manufacturer's instructions.
• Use appropriate eye protection and effective dust controls.
• Avoid breathing gemstone and abrasive dust; use suitable wet methods or extraction where required.
• Keep hands, hair, jewellery and loose clothing away from rotating components.
• Never change settings or clean the machine while the lap is moving.
• Keep electrical equipment and connections protected from water.
• Stop the machine and wait for all moving parts to stop before adjustments.

11. Continue Learning with SunMoonBay

Review the previous lessons and gemstone guides to strengthen your understanding before cutting valuable material.

• Step 1: Start the Gem-Cutting Course
• Step 2: Beginner Gem-Cutting Equipment
• Step 3: Planning a Gemstone Cut
• Step 4: Gemstone Faceting for Beginners
• Sapphire Inclusions Guide
• Sapphire Colour Guide
• Sapphire Refractive Index Guide
• How to Buy Natural Sapphire

Frequently Asked Questions

What does a faceting angle mean?

It describes the intended orientation of a facet relative to the machine's reference plane. The machine manual explains how to interpret its angle scale.

What is an index gear used for?

It controls rotational positions around the gemstone so facets can be placed according to a design. The gear must be compatible with the design's index instructions.

Are the same angles suitable for sapphire and quartz?

Not necessarily. Different gemstones have different optical properties, and designs also vary. Choose a suitable design rather than copying angles from an unrelated stone.

Why are meet points important?

They help establish the intended facet pattern, symmetry and outline. Accurate junctions also make it easier to evaluate the cutting progress.

Should beginners start with natural sapphire?

It is generally better to practise on suitable, inexpensive material before working with valuable sapphire rough. Learn machine control and design reading first.

SUNMOONBAY — LEARN STEP BY STEP

Your Next Step in Gemstone Cutting

You now understand the basic purpose of faceting diagrams, cutting angles, index settings and meet points. Continue practising with a suitable design and material before moving to valuable rough gemstones.

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