Rating Sea Glass
While there is a set standard for grading sea glass, it is important to note that the value comes in the find. A piece that may not have any momentary value, may have substantial personal value. Each piece that you picked up appealed to you in some way. Every piece you found comes with its own story or memory.
Sea Glass is rated based on a 4-point quality scale:
1) The Colour
2) The Shape, size, and thickness
3) The Frosting
4) Distinguishing marks
This will then determine the grade of the sea glass.
The most common standard colour chart for sea glass is the Carter Sea Glass and Rarity Chart, however there are many other charts online.
Common Colours: Kelly green, brown, white, and clear
Less Common Colours: soft green, soft blue, forest green, lime green, golden amber, amber
Rare or Uncommon Colours: pink, aqua, cornflower blue, cobalt blue, opaque white, citron, purple/amethyst
Extremely Rare: orange, red, turquoise, yellow, black, teal, gray
If you'd like to try your hand at sorting based on exact colours versus colour groups, the following website may help.
Once the piece of glass makes its way up on to show and dries off, you should be able to see some frosting, a crystalline formations. Due to the ph-levels of the water and sun exposure, the glass breaks down. More often than not, the frostier the glass the older it is. This process is called hydration.
The Shape, Size, and Thickness
While many pieces of sea glass are thin, a general rule of thumb is the thicker it is, the older it is. Often times dues to the repetitive motion, the sea glass also starts to develop curves or rounded edges. If the tides are in your favour, perhaps you will stumble upon a sea formed marble. (I have yet to find one.)
Shape can also refer to the type of sea glass you've found, and not just the natural occurring tumbling process. By this I mean you might find bottle tops or even bottoms. Perhaps you are lucky enough to stumble upon a complete vintage pieces. You might even find old marbles, bottons, stoppers, beads, safety glass, kick-ups, or even full pieces.
Due to the constant friction with the waves and shore lines, sea glass often looses its natural markings. Pieces that do still have markings are definitely much easier to date and also identify.
I did find a couple of links to hopefully help: