It is perhaps not discussed much, but the fine art of sponging to print a lithograph is not just water and a sponge. There are a number of aspects that move it from wiping up water to what makes lithography work.

 

The Sponge

Choose a sponge that is cellulose. They are inexpensive and hold a lot of water. Avoid the sponges that are made of foam. They hold a lot of water but are not absorbent and do not pick up enough water to give a good water film. Sponges should be washed out right out of the package because the manufacture puts a material in them that keeps them from drying out in the package. (No one likes to buy hard sponges.) Tip: If you trim the edges of the sponge so they don't have square edges, they will not snag the ink or shed quite as readily. The sponge will move along the plate or stone more easily and make sponging quicker and more efficient.

 

The Problem:

Sponge Streaks:

 Sponge streaks can appear at almost any time. They manifest themselves as strange marks in the ink, and in the print, that look like streaks made from poorly cleaned glass. They can run in any direction and may come and go depending on the consistency of the water film. Transparent inks are very susceptible to sponge streaks as the transparency allows you to see variations more easily. It is possible to even have sponge streaks show up in black ink, but for the most part, the problem is easily remedied.

 

The Solution:

Streaks are caused from water reacting with the ink and leaving telltale spots behind. The less ink there is on the image the more susceptible it is to streaking. For this reason, an image should not be left wet without a protective layer of ink to reduce streaking and water burns. After pulling a print, put a quick pass of ink on before you look at the print. It helps a lot. This first pass is also critical because it is where most of the streaking occurs. The first pass of ink after pulling a print will often determine if streaks will be present. The water film should be as thin as possible. If streaks are showing up, the image surface should be as dry as possible and still be wet,. After this first pass it is not as critical, but it doesn't hurt to alternate your sponge pattern, so that you are not always ending the sponging cycle in the same direction. This will keep streaks from being reinforced by repetition.
When sponging, remember that to get a good water film, you have to pick up all the water you put down so don't flood the surface. You'll just have to pick it up again, and it will be harder to keep the water film thin enough. Put down just enough water to wet the image and be picked up again quickly.

 

Dry Roll:

Too much water causes streaks and not enough water causes dry roll. Dry roll is caused when the printing surface becomes too dry allowing ink to stick to non-image areas. Dry roll shows up as small areas next to lines or in corners but can also happen on margins that have dried out. If you do get a little dry roll, or even a lot, not all is lost if you act. Sponge the image fairly wet. (At this point we are not concerned about streaks!) Try not to lift the ink with the sponge, it will just cause a mess. After sponging, roll the image as quickly as possible in a back and forth motion. The ink should lift up like magic. If it doesn't all come up, sponge the image again and roll it again. Tip: To avoid dry roll on hot dry days when the water is evaporating quickly, try putting ice in your water. The reduced temperature keeps the water from evaporating as quickly. Putting a cap full of glycerin in a bowl of sponging water will also help prevent dry roll and streaks.