Blueprint/blueline paper (technically, diazotype paper) is a paper that has been treated with chemical salts to give it a sensitivity to light, especially blue light.

howstuffworks.lycoszone.com has the following description of how it works:

In the diazotype method, the paper is light-sensitized with a mixture of a diazonium salt (used in the manufacture of dyes), a reactant, and an acid that keeps the diazonium salt and the reactant from reacting with each other. The semi-transparent original is placed on top of the sensitized paper, and a copy of the same size as the original is made by direct contact. Light destroys the diazonium salt. Ammonia gas or solution is used as a developer after exposure – it neutralizes the acid and allows the remaining diazonium salt to combine with the reactant to create a blue dye. The chemicals on the paper acquire color only in the areas not exposed to light. This diazotype method produces dark lines on a white background, and is the popular method used today for reproduction of large-format drawings.

The paper is especially sensitive to blue light and light with a large blue component, but is particularly insensitive to orange and yellow light. This makes the paper an interesting medium for landscape photography with yellows, oranges, and blues.

Several ‘speed’ ratings of paper exist, but I’ve only purchased 5 speed paper. I have been told by several shops that 7 speed paper is much quicker to expose, but the image quality is noticibly lower than with 5 speed.

Blueprint Paper is surprisingly cheap and readily available, even given the fact that many print shops have moved away from blueline methods and gone completely digital. However, it is very likely that a local shop will either have it or know where to get it. I pay between $30-$35 for 100 sheets of 36”x24” five speed paper.

If you have trouble finding it, contact A & E Graphics Complex and ask them for their pricing. If you STILL can’t get any, email me using the contact form and we can probably work something out for a few sheets.