"Eye-Clean" refers to the clarity of moissanite and some other gemstones. This means, broadly, that when looking at your moissanite (or diamond) inclusions are not visible to the naked eye. Under a microscope, however, you may be able to detect small inclusions.
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An eye-clean moissanite is not a bad gemstone—it is just as brilliant and sparkly as its VVS1-VVS2 diamond counterparts to the naked eye (which of course is how you will most frequently see the ring in your day to day). The presence of small inclusions, if invisible to the eye, is an excellent way to save money on your gem while not sacrificing beauty.
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