SI Diamond: The Eye-Clean Guide to Slightly Included Clarity

What Is an SI Diamond?

SI stands for Slightly Included — the fifth tier on the GIA diamond clarity scale, below Flawless, IF, VVS, and VS. SI diamonds contain noticeable inclusions under 10x magnification, but the critical question for most buyers is whether those inclusions are visible to the naked eye. The answer varies significantly between SI1 and SI2 — and between individual stones within each grade.

SI clarity is where the most interesting value opportunities exist in the diamond market — and where the most careful evaluation is required.

SI1 vs SI2: A Critical Distinction

SI1 (Slightly Included 1)

SI1 inclusions are noticeable under 10x magnification but are usually not visible to the naked eye, particularly in round brilliant diamonds. SI1 is often considered the lowest "safe" clarity grade for buyers seeking eye-clean stones — but it requires evaluation of the specific stone, not just the grade.

In round brilliants, the majority of SI1 diamonds are eye-clean. In step-cut shapes (emerald, Asscher), SI1 inclusions are more likely to be visible and should be evaluated carefully.

SI2 (Slightly Included 2)

SI2 inclusions are easier to see under 10x magnification and may be visible to the naked eye, depending on their type, size, and location. Some SI2 diamonds are eye-clean; others have clearly visible inclusions. SI2 requires careful stone-by-stone evaluation and is not recommended for step-cut shapes.

What Inclusions Are Found in SI Diamonds?

SI inclusions are more varied and larger than VS characteristics. Common types include:

• Crystals: Mineral crystals that may be visible as small dark or white spots under magnification, and occasionally to the naked eye in SI2
• Feathers: Small fractures — at SI grade, these may be more prominent. Location matters: feathers near the girdle or table are more visible than those in the pavilion
• Clouds: Groups of pinpoints that can create a hazy appearance if large enough
• Chips: Small surface breaks, typically at the girdle or facet edges
• Cavities: Small openings on the surface of the diamond

How to Evaluate an SI Diamond for Eye-Cleanliness

Because SI clarity requires stone-by-stone evaluation, here's a practical framework:

1. Request high-resolution images or video: Reputable online retailers (James Allen, Brilliant Earth) provide 360° video and magnified images. View the diamond face-up at normal viewing distance.
2. Check the GIA clarity plot: The inclusion map on the GIA certificate shows the location and type of inclusions. Inclusions near the center of the table are more visible than those near the girdle or in the pavilion.
3. Assess inclusion type: Dark crystals and chips are more visible than feathers or clouds. White or transparent inclusions are harder to see than dark ones.
4. Consider the shape: Round brilliants mask inclusions most effectively. Step cuts reveal them most readily.
5. View in person if possible: The ultimate test is your own eyes at normal viewing distance.

SI Diamonds by Shape: Recommendations

• Round brilliant: SI1 is usually eye-clean and offers excellent value. SI2 requires careful evaluation but can yield beautiful stones at significant savings.
• Oval, cushion, pear, radiant: SI1 is the recommended minimum. Some SI1 stones will be eye-clean; evaluate carefully. SI2 is risky.
• Emerald, Asscher (step cuts): SI1 and SI2 are generally not recommended. The open facet structure makes inclusions much more visible. VS2 or better is advised.
• Princess cut: SI1 is often eye-clean. SI2 requires careful evaluation.

The Value Case for SI Clarity

SI clarity — particularly SI1 in round brilliants — can offer significant savings compared to VS grades:

• SI1 typically costs 15–25% less than VS2 of equivalent cut, color, and carat weight
• On a $6,000 diamond, that's $900–1,500 in savings
• If the SI1 stone is eye-clean (which most round brilliant SI1 diamonds are), you get identical visible beauty at a meaningfully lower price

The key is evaluation. Don't buy an SI diamond sight-unseen without high-quality images or video. The grade tells you inclusions exist; only visual inspection tells you whether they matter.

SI Diamonds and Lab-Grown Alternatives

If budget is the primary driver toward SI clarity, consider lab-grown diamonds as an alternative. Lab-grown diamonds are available in VS and VVS clarity grades at prices comparable to or lower than natural SI diamonds — offering higher clarity at similar or lower cost.

The Authentic Beauty of SI Clarity

In crystal healing traditions, inclusions are understood as the natural signatures of a diamond's formation — the record of its journey from deep within the Earth. An SI diamond wears its story more openly than a VVS stone. Its inclusions, though minor, are part of its identity. For practitioners who value authenticity and the energetic richness of a stone with genuine geological history, an SI diamond's character is not a flaw but a feature — evidence of a stone that has genuinely lived, genuinely formed, genuinely arrived.

Final Thoughts

SI clarity offers some of the best value in the diamond market — but it requires more careful evaluation than higher grades. For round brilliant diamonds, SI1 is often eye-clean and represents an excellent value choice. Always evaluate the specific stone through high-quality images, video, or in-person inspection. The grade is a starting point; your eyes are the final judge.