Some diamonds that have fractures or unsightly imperfections are improved using a process called clarity enhancing (C.E.). This is where the imperfection, fracture or chip is filled with a carbon substance or some other clear filler so as to appear that the diamond has no imperfections.
Few if any of the laboratories will certify clarity enhanced diamonds, and if they do, the clarity enhancement should be clearly noted on the laboratory report.
C.E. diamonds definitely cost less than their non-enhanced counterparts. However, C.E. diamonds have been known to chip, split and fracture over time, as the substance that they are filled with is either not as strong as the diamond (carbon) itself or if carbon is used, then it does not bond strongly with the diamond.
If you have taken a liking to a diamond that is already set, be sure that there are no hidden flaws under any of the prongs of the setting. Check the laboratory certificate for the imperfection map of the diamond which will illustrate where all of the flaws are.
