acrylkic black background changes color

Angle of incidence is equal to the angle of reflection, putting black behind the subject will reflect black onto the surface. Try it with the light from the top, it is also important to control the spill of the light from hitting the black reflector. A cpl won't help unless the light source is polarized, i.e. the sun or a filtered artificial light.

now i understand, thank you

Wilt wrote in post #5598180
that's exactly what I was posting about in message #8 !

Not really... the black is reflecting FROM the surroundings. It is a reflection of a white background. It is not bouncing the light to the surroundings.

YOU can get the 'float' useing all flat black as well. the floor does not have to be reflective.

Mark1 wrote in post #5600189
Not really... the black is reflecting FROM the surroundings. It is a reflection of a white background. It is not bouncing the light to the surroundings.

I also mentioned the fact that the black plexi, if you had replaced it with a mirror, served to see the surroundings which had light cast upon them! Two different concepts mentioned in my earlier message, but I can understand how someone might not realize there were two different points made.

You don't need a mirror when the plexi is already reflective. I guess that is where you gave mixed signals.

Mark1 wrote in post #5604018
You don't need a mirror when the plexi is already reflective. I guess that is where you gave mixed signals.

I had mentioned about imagining the use of a mirror (instead of plexi), and you would then easily see the reflections of the surroundings that are going to be seen in the reflections on the plexi.

OK I got you I think. I was thinking you meant use a mirror and a black background for the shot. I dont know where I went off track!