Printing with Sodium bicarbonate I'm going to be 'printing' with a baking soda and water solution. I need to apply the solution to a surface that will hold it long enough to lay a piece of paper on it and saturate particular areas of the paper, the letter forms. What is the best surface to use. I've contemplated sponge, but am not sure if the sponge will gather enough solution intact to leave residue of the letter form or whole word on the paper when it dries. I'll find that out by experiment but would love any help that might improve my chances of success. This is for a college typography class.

Update:

Well, I've cut the letter forms out of sponge and adhered them to a sheet of Plexiglas. I originally wanted the sponge to sit in the bicarbonate solution and continuously wick it to the top of each sponge letter form. I've done some trials already however on this smaller version I've put the solution on the sponge letters, first with a brush, and recently with an eye dropper. I'm letting the paper dry at the moment.

I'm printing a form of 'Secret Ink'for a graphic design class. If I go with this project I'll have to make 28 posters, minimum 18" x 24" or larger this way.

Thank you all for taking the time to contemplate the problem and come up with solutions.I'll post pics of the results if I can.
Are you limited to a mixture of baking soda and water?  If you add a thickener (like agar gum) to the mixture to give it a bit more "stickiness," then you should be able to use rubber stamps (or foam cut-outs, etc...just google "DIY rubber stamps" for alternatives).  Use a foam brush to apply the liquid mixture to the stamp and apply to your paper.  

You will have to experiment with different thickeners (agar gum was just the first one that came to my mind) and amounts to determine what will work best with the baking soda and water mixture.