Recently a customer asked me to give them some select pictures in black and white, I said, sure, let me give you all your pictures in two versions, one in black and white, and one in color (I usually do not do this, but this is a smaller session and therefore less pictures to process). Here is a tip on the fastest way I know of to do such a conversion.
1. In library mode select all pictures by doing ctrl-A or (cmd-A in Mac)
2. On the photo menu, select “Create virtual copies”
3. In the library module’s filter by section, click on the “virtual copies” icon, this will show only the virtual copies and not the original pictures.
4. Open one of the pictures, and type “V” to convert to grayscale
5. Sync or copy and paste this edit to all the pictures back in the library module
Voila, you have just bulk converted all the images into black and white in 1 minute. Adjust individual picture to taste.