Sorry about the miscommunication. To clarify:
Melinex 990, an opaque white polyester, was used as the base for Ciba/Ilfochrome (7 mil) and some UltraStable (9 mil) prints. The clear polyester did contain a small amount of transparent white pigment (TiO2) but was extruded in such a way that "soap like bubbles" were formed that reflected, rather than transmitted, visible light thus causing the clear polyester sheet to appear "white".
Another feature of the 990 was the "Bexford Sub' - a thin layer of gelatin applied "in-line" (as the polyester was being made) at ICI's Bexford plant. This subbing layer was designed to receive and anchor subsequent coated layers to the polyester support.
As you know, gelatin stress increases with film thickness, and high relief carbon prints are particularly susceptible to cracking and base lift-off. After the Bexford plant blew up in the late 1990's the in-line gel sub was no longer available, other subbing techniques (corona discharge, chemical etch, off-line gel layer, etc) were tested but all showed signs of adhesion failure and UltraStable discontinued offering a White base. The adhesion performance of these new sub subbing layers, however, were suitable for Ilforchrome
Last edited by CMB; 09-24-2012 at 08:43 PM. Click to view previous post history.