A right-angle glass prism can turn a beam by total internal reflection — no silver to tarnish. Porro stacked two of them in 1854 so a binocular could be short and still erect the image. The Porro prism binocular is that pair in a Z.
This bench is the simpler turn: two prisms, white through, a screen at the end. TIR only holds if the hypotenuse is clean and the angle is right. Tilt past that and the beam starts to leak.