RE: make a female mold from an existing glass cowl?
Yes, you can use just about anything as a " Plug". For best results you would want to finish it off with as perfect a paint job as you can. Preferably an epoxy paint. Then you can mount it to a flat plate and then make a devider plate that seperates the two halfs. The plates need to be a non-porous material. I have had great results using balsa and then covering it with Monokote. Then wax one side with part all wax and apply PVA mold release. Let that dry overnite and then apply a couple coats of resin allowing then to cure before the next. You can add some tint if you wish. Once you have a good surface coat it's time to start applying cloth. You will want to make a paste with the resin, milled fiber and cabosil and fillet the corners. Usually 1/4" is fine and then start with the cloth. On a mold that size I usually go 6-8 layers of 4 oz. After the first side cures, remove the seperator plate and wax/PVA for the second side. Lay up the second side the same as the first. Let cure, seperate the two halfs and you have a right and left mold. Wax 6 times, PVA and make a part.