Some type of accurate carat scale is a must if you are planning on buying or dealing in a lot of loose diamonds or colored stones. If you are strictly going to be buying and selling mounted diamonds and other precious or semi-precious stones, a scale would be secondary, since a stone must be loose in order to be weighed. Later on we will discuss in detail the methods of weight estimation, but for now, we will focus on the general aspects of weighing loose diamonds.
There are many scales to choose from but the two main classifications are balance and electronic. Naturally the electronic scales will give you faster readings but the extremely accurate variety (to 1/1000th of a carat or .001 carat) can be relatively pricey for the newcomer or budget-minded dealer. Some scales offer the option of weighing pennyweights (dwt) and grams along with carats.
The balance scale offers something usually much more affordable. Some dealers from the old-school still use balance scales over the more popular and quicker electronic scales. The most basic balance type is simply placing the stone in question in the pan to one side and placing the counter weight(s) on the other until the indicating pointer has centered on the index plate. Along with larger, professional models, this is also the way a typical portable balance scale would work.
The more sophisticated balance types would include the rider and chain scales. The rider has weights that move or ride across a scale which is attached to a beam. Some scales measure just points and the even carat counterweights must be added to achieve a weight over 0.99 carat and in other scale models, the carat increments are included in the design.
A chain balance is similar in operation to the rider, but it uses a chain as the counterweight. On some models a control knob is used to adjust the chain until the pointer indicator is at zero or the center of the index plate. Again some models can be used with additional loose counterweights where others are designed to operate without.
Electronic scales are fast, accurate and are coming down in price as most electronic products do in this day and age. Electronic scales translate the weight on the platform into pressure, then into tension, which creates electrical resistance, which then indicates the exact weight of the subject in question. These scales are the most sophisticated and can be relatively expensive, but with some shopping and research you will find the scale that meets your needs. Always read the owners manual carefully and take your time when first using a new instrument to avoid what could be costly mistakes.