These are beauties. Front surface has a gold coating. Light reflection appears gold but if you look thru it it the image appears blue. Looks like about 50 percent reflection and 50 percent transmission. 50.7mm long by 22mm wide by 1.4mm thick. These are used in education, astronomy, microscopy, and with lasers. We don't have any more specifics for this and our price reflects the lack of more data. Omega sells a similar looking one for over $30 each. At our price you can have some for your friends, associates, and students. Get everyone's creative juices going. One of our customers supplied these thoughts: "I think you'll find that the beamsplitters are actually dichroic beamsplitters. They function as a combination of high-pass filter and low-pass filter." Thanks for the suggestion, Rick.