Even using the simple watermarking method described, it can be difficult to distinguish some watermarks. Watermarks on stamps printed in yellow and orange can be particularly difficult to see. A few mechanical devices are also used by collectors to detect watermarks on stamps such as the Morley-Bright watermark detector and the more expensive Safe Signoscope. Such devices can be very useful for they can be used without the application of watermark fluid and also allow the collector to look at the watermark for a longer period of time to more easily detect the watermark.
There are Southworth Papers available that have been manufactured ECF (Elemental Chlorine Free). Chlorine has traditionally been used to give paper its white appearance and to remove lignin, an element of wood fiber that yellows paper. Elemental Chlorine Free (ECF) papers are produced from pulp that has been bleached with a chlorine derivative such as chlorine dioxide, but without elemental chlorine. The use of ECF bleaching is an excellent technology choice for sustainable pulp and paper manufacturing. It eliminates the formation of dioxin, it allows for a greater yield of pulp, and it creates a stronger, more sustainable and recyclable product. The . Environmental Protection Agency (EPA) recognizes elemental chlorine free (ECF) bleaching as a “best available technology.”