Tween 20 ™
Handcoated Photography's Magic Bullet
By Dick Sullivan

Tween 20 ™, also known generically as Polysorbate 20 is a surfactant and spreading agent. First proposed for use in handcoated photographic printmaking by Dr. Michael Ware of the U.K. It is used extensively in industry but is usually confined to pharmaceuticals and other high-end applications due to its cost. Tween 20 ™ allows more emulsion to be put on the paper without the streaking and flaking that are normally associated with heavy coating. Tween 20™ almost always eliminates any need for double coating.

Individual conditions will dictate different amounts of Tween 20 ™. The biggest determining factor is the paper but humidity, material being coated and personal taste are also factors.

A good starting point is to use one drop of Tween 20™ 50% per 8x 10 print. Add it to the emulsion and thoroughly mix it in. If you are using a shot glass or small plastic container, swish the contents about for a few seconds. If the material is not mixed in thoroughly, when you pour it on the paper to coat, it will leave small marks where the emulsion has over penetrated the paper.

Coat the paper as you normally would, you should notice a subtle difference in the spreading. It should be smoother and more even. You may be able to coat a little wetter than you are normally used to. With most non-silver processes a little heavier coating will give better blacks. When you are finished coating, the paper should be wet and shiny but not runny wet.

Now let the paper rest. This will allow the Tween 20™ to "pull" the emulsion into the paper. During the resting phase the print surface should go from a shiny to a suede like appearance. This resting phase should take about 1 to 2 minutes.

The trick to getting a good coat of emulsion on paper is to get enough on and to get into the fibers of the paper. If it is too much on the surface, like glaze on a plate, it will wash off during development and leave a grainy, mottled, or flaky appearance to the final print.

Some authorities recommend the use of Kodak Photoflo ™, which does help the emulsion penetrate the paper, but it tends to do it to fast and causes streaking. Tween 20™ acts quite differently from Photoflo.

The 50% solution good for prints 8x1 0 and larger, for smaller prints you may want to dilute it to a lesser dilution of 25%, 10% or 5%. For traditional developing out platinum and palladium printing, some workers are recommending a fairly dilute stock solution of 2%.

For the eternally curious, the real chemical name of Tween 20™ sorbitan mono-9octadecenoate poly(oxy-1,1-ethanedlyl) Now say that 5 times with a mouthful of crackers.

August 30, 1998 --- Note!
We have discovered that Tween 20 in dilute form grows mold. We recommend buying it in concentrated form and mixing the 10% from that and periodically throwing away the old 10%.

Note: March 25, 1999
We are less enamored of Tween's effects now than we were earlier. It seems to introduce as many problems as it solves.