Diaphaneity is the catchall term for opaque, translucent, or transparent. Opaque means that when you shine a light through the object, it doesn’t shine through to the other side (like a piece of metal). Translucent means that the light does shine through to the other side, but you can’t see anything else the object (like tissue paper or cloth). Transparent means that you can shine a light through the object and you can see things through it (like a windowpane).
An opaque red bead looks different from a translucent or transparent red bead, and people in the past would have made conscious choices between the two. An opaque bead also generally has a different chemistry than a translucent one, because glass is naturally translucent or transparent; you have to add specific materials to turn glass opaque (such as antimony, tin, or bone).
I record diaphaneity in a separate column than color, using the abbreviations “op” (opaque), “tl” (translucent), and “tp” (transparent). This is usually fairly simple, though there may be questions about the line between transparent and translucent. Basically, I only use transparent if I can clearly see objects through the bead and I can tell what objects I’m looking at. It doesn’t matter if the object is wonky or fuzzy or whatever, so long as I can make out what it is.
If I can’t tell what the object is through the glass, then I label it translucent. In reality, I rarely use the transparent label – such beads are fairly rare. Opaque beads are simple, because when you try to record their color with LED backlighting, they don’t change at all. Note: Even if the color doesn’t change with LED backlighting, still record the color under both lighting conditions!
When documenting polychrome beads, you should record the diaphaneity of each color. While this may seem a bit overkill at first, you’d be surprised how many beads have an opaque core with a translucent shell or a translucent core with an opaque design. To help out your fellow bead researchers (and yourself), record the diaphaneity of each color.
You may come across a bead that appear opaque, but is actually translucent glass with lots of small bubbles to make it look opaque. This is relatively common in European beads, and may be prevalent elsewhere. The glass will most likely still be largely translucent, but it’s worth writing about the bubbles in your notes.