Step 3: Planning the Cut – A Beginner's Guide to Evaluating Rough Gemstones

Welcome to the SunMoonBay 7-Step Gem-Cutting Course. Before a gemstone reaches the faceting machine, a cutter must decide how to transform the rough material into an attractive finished stone. Good planning can help preserve colour, avoid unnecessary material loss, manage inclusions and improve the final appearance.

This lesson explains how beginners can examine rough gemstones, choose a suitable cutting design, estimate potential yield and prepare a practical cutting plan.

1. Why Planning a Gemstone Cut Matters

Rough gemstones rarely arrive in the exact shape needed for a finished gem. A natural crystal may have an irregular outline, uneven colour, surface damage, internal fractures or areas of unwanted material. Cutting and polishing can reveal its beauty, but every decision affects the result.

Removing too much material can reduce the finished stone's weight. Choosing the wrong orientation may produce an unattractive colour appearance. Ignoring a fracture can lead to breakage or cause a crack to extend during cutting.

A well-planned cut balances several objectives:

• Beauty: Create attractive colour, brightness and light return.
• Durability: Avoid leaving vulnerable points, open fractures or excessively thin areas.
• Yield: Preserve as much suitable gemstone material as practical.
• Cutting feasibility: Select a design that matches the rough stone and the cutter's skill level.
• Value: Consider the finished stone's appearance, size, quality and intended market without assuming that higher weight always means higher value.

The best design is not necessarily the largest possible cut. A smaller, well-proportioned gemstone with attractive colour and good clarity may be more desirable than a heavier stone with poor proportions or visible damage.

2. Identify the Rough Gemstone Before Cutting

Begin by identifying the likely gemstone species and checking whether the material is suitable for the intended cutting process. Different minerals have different hardness, toughness, cleavage, optical properties and cutting requirements.

For example, sapphire and ruby are varieties of corundum. They have a Mohs hardness of 9 and no true cleavage, although they can still fracture or chip. Some other gemstones have more pronounced cleavage, which can make cutting orientation especially important.

Do not identify a stone by colour alone. Blue rough material could be sapphire, spinel, glass or another mineral. Use several observations and appropriate gem-testing methods when necessary.

• Observe the external crystal shape and surface features.
• Check colour under neutral, consistent lighting.
• Examine transparency and visible internal features with suitable magnification.
• Record the rough stone's weight and dimensions.
• Consider professional identification if the species or treatment status is uncertain.

3. Examine Colour and Colour Distribution

Colour is one of the most important factors in planning a coloured gemstone. Rough material may show different colour zones, pale areas, dark patches or colour concentrated near one end of the crystal.

Before deciding where to cut, rotate the rough stone under consistent lighting and examine it from several directions. Record where the strongest and weakest colour appears. Consider how the finished stone's face-up colour may change when its orientation and depth change.

Questions to ask about colour

• Is the colour evenly distributed or concentrated in certain areas?
• Does the rough appear too dark, too pale or attractive at different viewing angles?
• Could a proposed orientation preserve a pleasing face-up colour?
• Would the design require excessive depth or sacrifice too much material?
• Could cutting across colour zones produce an uneven appearance?

For blue sapphire, for example, the objective is not simply to retain the largest volume of blue material. The cutter must consider colour intensity, tone, saturation, brightness and how the finished gemstone will look from above.

Never assume that rotating a stone in a particular direction will guarantee a specific colour result. Optical behaviour depends on the gemstone, its colour distribution, lighting and final cut proportions.

4. Inspect Inclusions, Fractures and Surface Damage

Inclusions are natural or other internal features within a gemstone. Depending on their type, position and extent, they may have little effect on the final appearance or may significantly affect transparency, durability and cutting decisions.

Use a suitable loupe or microscope and examine the rough stone from multiple directions. Look for cracks, cavities, cloudy zones, mineral crystals, healed fissures and areas that appear structurally weak.

What to look for

• Open fractures: Cracks that reach the surface and may create weak points.
• Internal fractures: Features that may affect durability or visibility after cutting.
• Cloudy areas: Zones that can reduce transparency or brightness.
• Mineral inclusions: Internal crystals that may be visible in the finished gemstone.
• Surface damage: Chips, cavities and weathered areas that may need removal.

Planning around an inclusion does not always mean removing it completely. Removing a large area may cause unnecessary weight loss. Instead, assess whether a different outline, orientation or cutting design can produce an acceptable result while maintaining structural integrity.

Some inclusions are attractive or diagnostically useful, while others are undesirable. Their importance depends on the gemstone type, intended appearance and overall quality.

For more information, read the SunMoonBay Sapphire Inclusions Guide.

5. Understand Crystal Shape, Cleavage and Fractures

The natural shape of a rough crystal can help determine the most practical finished outline. However, following the crystal's external shape without considering internal structure can lead to a poor result.

Some minerals have cleavage: a tendency to split along particular crystallographic planes. Other gemstones lack true cleavage but can still break along fractures or develop chips under stress.

Before cutting, consider:

• The direction and shape of any visible fractures.
• Whether the rough material has cleavage that could affect orientation.
• How much material must be removed to create a stable outline.
• Whether the planned design leaves sharp, thin or vulnerable sections.
• Whether the stone can be secured safely for cutting.

Never force a stone through a cut when it shows signs of cracking or unstable mounting. Stop and reassess the plan if the material behaves unexpectedly.

6. Measure and Record the Rough Stone

Accurate measurements make it easier to compare cutting options and estimate potential finished size. Record the rough stone's weight in carats, length, width and depth in millimetres. Note visible colour zones, fractures, inclusions and the direction of the proposed table.

Use a calibrated gemstone scale and suitable measuring tools. Handle small or valuable rough material carefully to avoid dropping or chipping it.

A simple written record is especially useful when comparing several pieces of rough material or reviewing your progress during practice sessions.

7. Choose a Suitable Faceting Design

Faceting is the process of cutting and polishing flat surfaces, called facets, at planned angles and positions. A design determines the arrangement of the table, crown, girdle, pavilion and other facets.

The right design depends on the rough stone's shape, colour, clarity, dimensions, optical properties and intended use. Beginners should prioritise a design that can be cut accurately with their available equipment.

Common design choices

• Round brilliant: A familiar outline with a carefully arranged facet pattern. It can provide attractive brilliance but may require substantial shaping from irregular rough.
• Oval: Useful when the rough material's shape suits an elongated outline. Proportions and symmetry require attention.
• Cushion: A rounded-square or rectangular outline that can suit some rough shapes and cutting objectives.
• Emerald or step cut: A design with broad, step-like facets. It can reveal clarity characteristics clearly, so rough quality and inclusion placement matter.
• Simple beginner designs: Designs with manageable facet sequences and published instructions can help new cutters learn accurate indexing, angle control and polishing.

No design guarantees maximum yield or the best appearance for every stone. Compare possible outlines against the actual rough material before choosing.

8. Understand Table, Crown, Girdle and Pavilion

Planning a faceted gemstone requires understanding its main parts.

• Table: The large upper facet, viewed from the top.
• Crown: The upper section between the table and girdle.
• Girdle: The perimeter separating the crown and pavilion.
• Pavilion: The lower section extending from the girdle toward the culet.
• Culet: The small bottom facet or point, depending on the design.

The angles and proportions of these parts affect light return, face-up colour, appearance and durability. A design must suit the optical properties of the gemstone, rather than simply copying the proportions of a different material.

Use a reliable faceting diagram or tested design for the gemstone being cut. Follow its specified angles and index settings as a starting point, then make informed decisions based on the material and the design's intended result.

9. Estimate Finished Weight and Material Yield

Cutting removes material to shape the stone and create polished facets. The finished gemstone therefore weighs less than the original rough. The amount retained depends on the rough shape, fractures, inclusions, chosen outline, cutting design and required proportions.

A useful first estimate is to calculate finished weight as a percentage of rough weight. This is only a planning exercise; it is not a prediction or guarantee.

The basic formula is:

Estimated finished weight = rough weight × assumed yield percentage ÷ 100

For example, 10 carats × 30 ÷ 100 = 3 carats.

Remember that yield alone does not determine profitability. A well-cut gemstone's value also depends on species, colour, clarity, treatment status, finished size, craftsmanship, market demand and reliable identification.

10. Plan the Orientation and Mark the Rough

Once you have examined the rough material and selected a possible design, decide how the stone should be oriented for cutting. Consider the colour distribution, inclusions, fractures, crystal shape and the amount of material that must be removed.

Where appropriate, mark the intended outline or reference direction using a suitable method that will not damage the stone. For valuable rough, an experienced cutter may use additional examination or planning methods before making an irreversible cut.

Before proceeding, check that:

• The proposed outline fits within the usable rough material.
• The design can accommodate the stone's visible structural features.
• The estimated dimensions are compatible with the intended finished shape.
• The cutting sequence is understood and the relevant diagram is available.
• The mounting and equipment are appropriate for the stone and operation.

Do not make major cuts based on guesswork. If the orientation or internal structure remains uncertain, obtain advice from an experienced gem cutter.

11. Prepare a Beginner's Cutting Plan

A cutting plan turns observations into a practical checklist. It does not need to be complicated. For each piece of rough material, record the information that will help you make consistent decisions and evaluate the finished result.

Keep your notes after cutting. Compare the estimated finished weight with the actual weight and record what worked well. Over time, these records can help improve your judgement when evaluating similar rough gemstones.

12. Common Beginner Mistakes to Avoid

Choosing a design before examining the rough

A favourite design may not suit the stone. Examine the material first, then select a design that fits its characteristics.

Focusing only on carat weight

Preserving weight is important, but not at the expense of a poor outline, weak structure or unattractive appearance.

Ignoring internal fractures

A fracture can affect both the cutting process and the finished stone's durability. Inspect the rough carefully and reconsider the plan when necessary.

Expecting every rough stone to produce a large finished gem

Natural crystals vary greatly. Material loss is a normal part of faceting, and some rough stones are unsuitable for a particular design.

Using unsuitable cutting angles

Angles influence the finished gemstone's optical performance. Use a suitable design for the gemstone species and avoid assuming that one set of angles works for every material.

Rushing the planning stage

Careful examination and measurement can prevent costly mistakes. Take time to understand the rough before using the machine.

13. Gemstone Education: Helpful SunMoonBay Guides

Continue learning about gemstone identification and quality using these related educational resources:

• Sapphire Inclusions Guide – understand internal features and how they affect appearance.
• Sapphire Colour Guide – learn about colour, tone and saturation.
• Sapphire Refractive Index Guide – learn about RI testing and its role in gemstone identification.
• Heated vs Unheated Sapphire Guide – understand an important aspect of sapphire treatment disclosure.
• How to Buy Natural Sapphire – review important considerations when purchasing sapphire.

Frequently Asked Questions

What is the first thing to do before cutting a rough gemstone?

Identify the likely material, examine its colour and internal features, measure its dimensions and weight, and assess any structural risks before choosing a cutting design.

How much weight is lost when faceting a gemstone?

Weight loss varies with the rough material, its shape and quality, the chosen design and the amount of material that must be removed. No single yield percentage applies to all gemstones.

Which gemstone cut is best for beginners?

A relatively simple design with a clear faceting diagram and manageable cutting sequence is a sensible starting point. The best choice also depends on the rough material and the equipment available.

Can inclusions be removed during cutting?

Some inclusions or damaged areas can be removed, but doing so may cause substantial weight loss. Others extend too deeply into the stone or may be better managed through an appropriate cutting plan.

Why does gemstone orientation matter?

Orientation can influence how colour appears, how inclusions are positioned and how the rough material can be shaped. Its effect varies with the gemstone and cutting design.

Can I estimate the exact finished carat weight before cutting?

No. You can calculate approximate scenarios, but the exact finished weight cannot be known until the gemstone has been cut and polished.

Conclusion: Plan Carefully Before You Cut

Successful gemstone faceting begins long before the machine is switched on. By identifying the rough material, examining colour and inclusions, understanding structural risks, choosing a suitable design and estimating possible yield, beginners can make more informed cutting decisions.

Remember the main principle: plan for the best practical combination of beauty, durability and usable weight—not weight alone. Careful planning, appropriate equipment and supervised practice help develop the skills needed for better gemstone cutting.