aloha ! the previous post talked about using the grid spot to control or modify the light.
one additional tool for modifying light is called dots and fingers. you can make your own (DIY) from adding black cards on old bicycle spokes or buy them from www.lowel.com/. by changing the opaque versus screens and varying densities allow you to further finesse the light.
you can see the previous image with two reflections on the rim of the shiny/translucent vessel.
by blocking the light that is falling on the rim with the small flag the photographer is able to control this wanted or unwanted reflection.
easier said than done.
i was challenged by using a flash/strobe that lacked modeling lights. in normal strobes there is a modeling light that allows the photographer to ‘see’ what is happening with reflections and changes in the modification of the light. see image below of the setup. 1/15 at f/5.6 iso 200
the image below demonstrates an example with the finger/flag that is too close causing a shadow.
below is the image using two fingers (tiny flags) to control the reflections/lighting bouncing back into the lens.