Well, turning black when fogged means that the emulsion can get there, but that the contrast is too low. That suggests that something is lowering the contrast.

How to up the contrast? Well, shorten the addition time of the Silver Nitrate as I said before, but then the pig gelatin may be a problem as often additives are put into the gelatin to alter its properties for the intended use. Bovine (cow) gelatin is more common for making. In terms of properties, the swell factor of each gelatin is different. Bovine gelatin swells more in the developer, while porcine gelatin swells more in the acid fixer or wash.

Hope these hints help.

PE