This Expert Columbia with serial number 4319 may well be one of the best preserved ordinaries in the Velorama Museum. Original paint and nickle, original lining in very good condition ... it's a dream.
Columbia started building the Expert in 1882. It was built until 1892 and has year-by-year minor changes. All these are documented in the very fine book 'Collecting and restoring antique bicycles', by Donald Adams.
The suspension saddle you see in the pictures was changed in 1886 by a Hammock of Kirkpatrick saddle.
The fixed step you see in the pictures was changed in 1888 by an adjustable step.
The rear fork was closed and tubular until 1884, you see it on the other Expert on this website.
Rear fork was semi tubular with a rounded crown (like the one you see in the pictures) in the years 1885 and 1886, it had a square crown in the years 1887-1892.
There are many more small changes, but these details make this bike the 1885 model.
Look at the very special, almost hidden place of the serial number. The front wheel size is indicated at the left side of the front fork crown.