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Picture of dreaming mouse - the blueprint for a giant cheese house!

 

Blueprinting

What's it all about?

A blueprinting mixture is very easy to set up, and we have found that many plain papers will successfully take up this mixture. Objects put onto the dried blueprinting paper will block sunlight from getting to the chemicals - these bits stay unchanged. Where the sunlight can get to the paper, an intense blue colour develops. The blue colour will not wash out of the paper, but the greenish colour left under the object will. This leaves a white image of the object on a blue background.

Lots of things can be blueprinted, such as pens, rulers and protractors, with great results. Our students have also experimented with cut-out messages and pictures, and some have tried to get different shades using masks and different exposure times. It works even on an overcast day in Harrogate!

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Preparing blueprint paper

 

Student notes

These are in two parts, making the blueprint paper and making the blueprints.

Making the blueprint paper

Put your gloves and goggles on, then follow the instructions. Get two small beakers, a measuring cylinder and a stirring rod. Weigh 5g of Substance A into one of the beakers, and 9g of Substance B into the other beaker. Use the measuring cylinder to put 50cm3 of water into each beaker. Stir carefully until all the crystals in both beakers have dissolved.

Do the next bit in a dark part of the lab. Mix the two liquids together, and pour them into a tray. Put a piece of white A4 paper into the liquid just long enough to get it damp - not wet! Your paper will turn greenish blue. Hang it up to dry out.

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Making the blueprints

Carry your prepared paper and object over to the window. Place your object on top of the paper, and leave it in the light. The bits covered by your object will stay green, but the exposed bits will turn blue. When you think it has gone blue enough, take the object off the paper. Wash the paper with water - this washes away the green bits leaving the blue behind. Leave your photograph to dry out. Wash your hands carefully.

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Teacher notes

This stage should be done away from direct sunlight. Two solutions need to be made: substance A (5g of potassium hexacyanoferrate(III) – Irritantin 50cm3 of water), and substance B (9g of ammonium iron(III) citrate in 50cm3 of water). The ammonium iron(III) citrate was tricky to track down, but we eventually obtained it from Sigma Chemicals.

The two solutions should be mixed together and poured into a tray. Plain A4 paper is then floated on the surface (a wide range of papers seem to work, but avoid very shiny papers or very coarse ones). We find that it works best if the tray is gently swirled to cover all the underside of the paper, without prodding it with fingers and pens! The paper should then be hung up to dry in a dark part of the lab, and then left flat in a drawer or lightproof box.

When the students are ready, they should arrange their objects or paper cutouts on the blueprint paper (it must be dry – it doesn’t work if the paper is damp). The assembly can then be left in sunlight on a bench to develop. It helps if a sheet of glass is placed onto to keep it all flat (a local glass company, W.D. Rollings Ltd, very kindly sold us A4 off cuts of glass with bevelled edges at a reduced price). After the blue colour develops, the paper is then washed with clean water to remove the undeveloped green colour, and then left to dry. In good light, the blueprint develops within a minute or two giving a sharp image; a very long exposure on dull days produces a shadowy effect due to the movement of the sunlight.

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Technician notes

For 5 groups of students:

10 x 150cm3 beakers
5 x 100cm3 measuring cylinders
5 x glass rods
5 x plastic trays
5 x wash bottles containing distilled water
Approx. 100 sheets plain A4 paper

On the side bench:

digital balance
potassium hexacyanoferrate(III) – labelled as “Substance A – Irritant
ammonium iron(III) citrate – labelled as “Substance B”
Drying line with bulldog clips

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