The reason that it is possible that diamonds can increase in value is because they are the strongest substance on earth. Diamonds are continuing to increase in value and are likely to do so for many years. How Well Do Diamonds Hold Their Value Quora A diamond that was purchased in 1970 would of course be worth considerably more in 2016. Do diamonds increase in value . The Value of Diamonds. Only an extremely small category of diamonds increase in value which we will discuss later. A diamonds value appreciates over time. If they do increase in value then the buyer can feel assured that they have made a suitable investment. With lab-grown diamonds there is an ever-growing supply but not an overwhelming demand. Unless you happen to own a rare fancy colored diamond or a one-of-a-kind 100ct DIF diamond most gem-grade diamonds do not increase in value over time. The increased demand and rareness of the colored diamonds have led to an increase in prices. The short answer...