Land's key patent filed in 1944, issued in 1950 US2500421

The USPTO was slow in issuing this patent by Land, which is understandable since it was abandoned and refiled, possibly with additional material as was the practice of the time.

We are studying this one today, mostly for the description of the preparation of the receiver sheet.

Here is the link to a pdf of US2500421

After reading this, one has to wonder if the titanium dioxide was thought of as a "nucleating agent" or even a particle.