Got a Series 6 orange looking filter with my Speed Graphic lenshade. I forgot its purpose.

Is this a warming filter for color film, or just a light orange filter for darkening clouds on black and white film?

What is the filter factor?

Thanks in advance.

For B&W use, sky darkening, haze cutting, filter factor around 2.5.

What pv17vv said. Wratten G (also known as no. 15) renders blue sky darker than "natural" on b/w panchromatic film. Wratten K2 (no. 8, light yellow) renders sky "natural" (i.e., presumably same contrast as the eye sees). Wratten A (no. 25, red) gives dramatic sky-cloud contrast. Each is useful depending on circumstances and goals; a set of these is a necessary part of the landscape photographer's kit.

While not usually found in a Speed Graphic kit, the G or No 15 is also good to use when shooting with half of a combination lens, like a Protar. Single cells usually exhibit some color fringing and the No. 15 cuts out a good portion of the blue.