Good question! If there is any silver left in the emulsion, then concentrated selenium toner, or Kodak IN-5 intensifier, should increase the density. If there is only dye left in the emulsion, you will be out of luck. I would try one negative with Kodak selenium toner diluted 1:2 with water for about 10 minutes with occasional gentle agitation and see what happens. If that works, but you need greater intensification, try the IN-5.(posted 9134 days ago)