Hand colored photographs of historical Japan

Here's another article I came across recently. It's interesting to note which parts of the photo the colorist chooses to imbibe color. I find the aesthetic pleasing overall. Would love to see more.

http://www.openculture.com/2017/07/hand-colored-photographs-from-19th-century-japan.html

Regards, Art

Lovely work, it reminds me somewhat of gum over palladium, the mixture of soft sepia tones with gentle colour on top.

Beautiful. It looks as if a very subtle layer is added to the complete photo as last layer to harmonize all the colours. This technique is sometimes also used in oil paintings (glaze painting).

I wonder if there are any publications where the technique for these photos is discussed.