You can safely make a mold using silicone. The silicone will not stick to the acrylic of the visor or the FRP reinforce. However, If you want to duplicate the visor, you would need to remove the FRP reinforce from you tool.
I would not try to "cast" this in resin, the chances of getting a usable part are pretty slim. Vacuum forming or blow-forming are your best options.
Vacuum forming can be done with a gypsum tool. You will not avoid distortion or "mark-off" no matter how smooth the tool is, but smoother is still better. I would make the v-form pattern in Hydra-stone, as it is very hard and can be preheated to give you a better part. If you vacuum form it, an have enough suction, I would recommend Acrylic over PETG, as it is harder, and easier to polish out imperfections.
Vacuum forming will give you "mark off" because you are contacting a cooler tool, with hot plastic. As soon as the plastic touches the tool, it will cool, and other areas, which are still hot, will continue to stretch, and thus change the material thickness in tiny uneven amounts. As soon as you have a thickness change, you make a "lens" that bends light, and gives you this distortion. If it's minor, it can be sanded and polished out. This is a tough part to v-form, as the sides (pivot points) are parallel and vertical. When you mold it, I'd brace the pivot points outward a bit, to help your v-form tool shape, making it easier to remove your part.
What is your intended use of the copy? If it is for a mercury helmet visor, then this is too large. This is the sun visor of a MK IV helmet, which is about a 1/2" larger radius than the clear visor. If you mold the outside of this visor, and pour you tool into the mold, you will add another 1/8" or so to the radius when you vacuum form it. This will make a visor that is 11/4" wider than a mercury visor.
If you are in need of a mercury visor, we may have some for sale in the next couple of weeks. These are surplus visors with minor damage or imperfections that we do not use. They typically sell pretty cheap, likely less than the materials you would purchase to make a copy of this visor.
