Amber is classified into translucent, transparent, semitransparent, and opaque. Low-transparent amber is called “bastard amber.” A fossilized resin that’s tainted with wood or any organic matter is graded based on its internal structure.
Jewelers usually prefer clear amber. However, translucent amber can look wooly, with some opaque sections. Assessing the value of amber requires a combination of the following factors: internal structure, outside appearance/quality, its age, and whether or not it contains entombed materials (e.g., bugs, bark, etc.).
Visible, but rare inclusions of entombed relics in amber can improve its price. Often, the resin is brought for assessment simply because of its inclusions, mainly because they are also proof of its authenticity.
The milky coloration seen in some amber pieces are a result of air bubbles and can be considered by some jewelers as defective. However, some jewelers make an exception. For example, a single large bubble can add value to the amber piece, since the bubble improves the play of color and light.