Lee Polyester Enlarging Filters 100 x 100mm
Old Packaging, as stock lasts
Enlarging filters are classified by density (graded 5 to 50) increasing in density (how much light it blocks) as the numbers increase.
The colour of the filter will also determine what colour is absorbed. If you are familiar with colour wheels, both the RGN and the CMY, you are good to go: basically the filter will absorb the colour at the opposite of the wheel and they can be combined, especially if you want to go from CMY to RGB.
As a quick guide:
Red absorbs blue and green
Green absorbs blue and red
Blue absorbs green and red
Yellow absorbs blue
Magenta absorbs green
Cyan absorbs red
So if you combine a yellow and a cyan you get the equivalent of a green filter as it will absorb both red and blue.