This is a lovely family photograph taken by H. R. Troopman of Chicago. The girls look to be 10 years old or so. I think the photo is from the 1880s, but what is tricking me is the slight purple tint it has. The collodion process was not widely used until the 1890s. I found another site with a Troopman photograph showing a soldier in about 1868. The date of this photograph is difficult to nail down.
UPDATE: Thanks to Iggy we now know this photographer was H. R. Koopman, thanks Iggy!!
From the Pullman (Railcar) State Historic Site:
“1884 — 1914: H. R. Koopman
Henry R. Koopman was the Pullman photographer of the town and workers.
In 1893 he published a book on the town called “The City of Brick”. His studio was located at 11106 S. Michigan Avenue in Roseland. From 1918-19, he worked in the Pullman Shops in the shell division. We have many original photographs, studio cards, postcards, etc. by Koopman as well as images of his studio in Roseland.”