Complex sentence: Some concern processes for making subtractive color transparencies, which do not require any special projection or viewing equipment; examples of these were preserved by Prokudin-Gorsky's family and have recently appeared online.
Split into simpler sentences: Some concern processes for making subtractive color transparencies, which do not require any special projection or viewing equipment. Examples of these were preserved by Prokudin-Gorsky's family and have recently appeared online.