The opening is described by the shape and cross sectional area. Cell wall- bridge is the surface of the cylinder between cells. The chemical etching of lines and dots through photo resist was the beginning of rotogravure. The carbon tissue method of image photo-transfer to a gelatin resist was discovered and perfected in the later quarter of 19th century. The same cell area, variable depth.
Carbon tissue is a water sensitive fibrous paper coated with smooth gelatin resist.
Tissue was etched by FeCl 3 ferric chloride- depth 45 micron, various screen counts. The resist is sensitized to light by submerging it into a potassium bichromate solution. The sensitized carbon tissue can be dried, and refrigerated until used in the photo-transfer process. Tissue is formed into a sheet sizes and wrapped around copper plated cylinder. A glass positive was used to expose the light sensitive gelatin.