I am using Photoshop to prepare a scan of a painting for printing. The print will have metallic ink added to certain parts of the image. The print shop has asked me to "create a spot color channel that covers any area you want enhanced by the effect." I am new to this and all of the resources I've found so far about how to do this involve selecting an entire color range and turning it into a spot channel. However, only a small amount of this image (not neatly selected by a color range, etc) needs to be added to the spot channel for the metallic ink, so it seems like it would be more efficient to manually mask or erase the image to isolate the desired areas. Can anyone offer advice on the best way to do this? Like, can I simply copy the image into a new layer, delete anything I don't want to be printed with the highlight, and make that the contents of an additional spot channel?