If the internet is to be believed they did not have one way mirrors in the 17th century. They were invented in the early 1900s.
However, looking at the patent for what is supposed to be the first it says that there were earlier attempts--they just sucked because making the partially reflective layer was difficult and expensive and not durable enough when used on outdoor advertising devices.
Yes, you read that right. Advertising. Technology being driven by someone's desire to show ads is not new.
The thing the inventor was building was a case for displaying advertising posters. The case had a glass front, and the poster was behind the glass, with powerful lights behind the poster. When the lights were off the glass would appear to people looking at the case to be a mirror. When the lights were on the poster could be seen.
Plain glass works fine for this, but they were perfectly capable of making one way mirrors at the time. The historical term is "half silvered mirror", which were used in a lot of early scientific research in optics.
However, looking at the patent for what is supposed to be the first it says that there were earlier attempts--they just sucked because making the partially reflective layer was difficult and expensive and not durable enough when used on outdoor advertising devices.
Yes, you read that right. Advertising. Technology being driven by someone's desire to show ads is not new.
The thing the inventor was building was a case for displaying advertising posters. The case had a glass front, and the poster was behind the glass, with powerful lights behind the poster. When the lights were off the glass would appear to people looking at the case to be a mirror. When the lights were on the poster could be seen.