Diamond Certificate vs. Appraisal
A diamond certificate or grading report is a document with factual information relating to that particular stone. The specifications mentioned here would include measurements, color, carat weight, internal characteristics, and clarity. This document also confirms that the diamond is real, as well as whether it has been enhanced in any way, and if so, how. Graduate Gemologists (G.G.) at reputed laboratories like GIA are responsible for certifying diamonds in this way.
Appraisals are different from this, in that they are simply an estimate of the monetary value of the stone, which can change based on quality, as well as market conditions. The certificate comes in handy when valuing a stone during an appraisal. The latter should be updated periodically to reflect market changes, while a certificate stays the same for any stone unless further treatment is done on it, in which case it needs to be sent in for another certification process.