1- One 110 cm by 100 cm plywood panel 18 mm thick. Cut a 120 degree angle on the 100 cm width.
2- Two metal angle strips ( v at 90 degree ), fix them with 2 or 3 screws under each side of the 120 degree angle. Provide oval holes for the screws to allow some play in fastening against the mirrors.
variation: cut a slit in the wood and fit the mirrors in.
3- Two mirrors ( 60 cm by 60 cm ) slide them vertically brtween the angle strip and the plywood. Each mirror reflect a different view of the back of the object.
4- Two rigid plywwood vertical blinds in polystyrene ( L80 cm, H60 cm, T2 cm ) to blank out the surroundings. Along the height of 60 cm cut a grooveat, at least, 2 cm from the edge and 1 cm deep. Slot the mirrors in the grooves.
Lighting: lighting from above is preferable in order to illuminate both front and back, with artificiel light or not. It is essential that both the fossil/mineral and the camera lens are placed precisely along the bissection of the 120 degree angle. It is advisable to use a zoom.
Once built, and it is simple to do because each part slides into each other, it is easily dismantled, allparts can be stored flat.