I was really tired tonight, so I practiced a bit with these Mexican Coca-Cola bottles.
I could have done this by doing two shots and merging them but that will be for another night.
SB600 with red gel firing in to white seamless poster sheet. I needed some fill light on the bottle cap so I set the pop-up flash to manual 1/128th. The mount
flash was decreasing the intensity of the red gel. I should have used another flash to highlight the bottle cap and control light spill.
There's much else which can be done but I'll do it later.