Tools of the Trade - 365nm UV Flashlight
By Selena Cate Green, Editor
The Secondhand Market Report
When sourcing vintage glass, not everything reveals itself under normal light. There is a hidden world of color. Clarity, and surface condition tell part of the story, but material composition often requires a closer look. This is where a 365nm UV flashlight becomes a useful field tool.
A 365nm ultraviolet light can reveal reactions in certain types of glass that are invisible to the naked eye. These reactions may offer clues about materials used, manufacturing practices, and, in some cases, the period in which a piece was produced. For those sourcing in thrift stores, estate sales, or private collections, this added layer of observation can support more informed decisions.
Historically, glassmakers experimented with a range of minerals to improve clarity, stability, and workability. Magnesium was used in some glass formulations to enhance structural stability and reduce cloudiness, contributing to a cleaner, more refined appearance. While magnesium does not create brilliance in the way lead does, it played a supporting role in improving overall glass quality in certain contexts. Whatnot is full of sellers boasting about the glow of glass.
Ultraviolet reactions in glass are influenced by multiple trace elements, which vary by era and manufacturer. A UV response should be considered one indicator among many—alongside weight, color, mold marks, wear patterns, and provenance—rather than a definitive test. The flashlight supports this.
In practice, a 365nm UV flashlight is compact, discreet, and easy to use. We carry the flashlight at all times in our bag or pocket when we are sourcing or researching. It allows for quick checks without drawing attention and is especially helpful when sorting through mixed lots or unfamiliar pieces. Over time, its value becomes less about what glows and more about recognizing patterns, exceptions, and context.
For readers interested in building a small, practical toolkit for sourcing, a Secondhand Market Report field tools list is linked on this page. It includes the 365nm UV flashlight referenced here, along with other everyday tools and products that we use.
As with all sourcing tools, context matters. A flashlight does not determine value on its own, but it can help prompt better questions—and in the secondhand market, asking better questions is often where real understanding begins.