MadSci Network: Chemistry
Query:

Re: How can one use solutions and chromatography paper to duplicate a picture

Date: Sat Sep 29 06:31:00 2001
Posted By: Harry Adam, Research Associate, Research Division, Kodak Limited
Area of science: Chemistry
ID: 1000575030.Ch
Message:

Hello, Angela  it is difficult to give you a full answer to your question 
without more information, but I will try nevertheless.
You do not say whether this is colour as opposed to black/white, or 
whether your original is a print or a negative. Chromatography paper has 
the property of easily absorbing solutions while calendared papers have 
glossy surfaces which make it difficult for solutions to absorb, I would 
guess ease of solution absorption is the reason for suggesting 
chromatography paper.
My best guess at what is suggested here is that you are making a print 
from a negative, by contact printing  i.e. shining light through the 
negative onto the print paper and then fixing the image. By contact 
printing, I mean that the negative lies directly on top of the paper, and 
so the copy of the image, the print exactly matches the size of the 
negative.
To do something like this you need to sensitize the paper to light, and 
the solution which does that most easily is silver nitrate. 
If you have access to silver nitrate, you need to be careful. Make sure 
your teacher is on hand to help. It is toxic, as well as light sensitive, 
and you do not want to get any on clothes or skin. Silver nitrate 
dissolves in water to give a colourless solution but it is unstable to 
light and will go black as silver precipitates on the action of light  so 
will skin and clothes!
I would guess that what you could do is soak the paper in a dilute 
solution of silver nitrate  in dim light. Store any solution in an opaque 
bottle clearly labelled  and when you have soaked the paper hang it up to 
dry in a dark place. When it is dry, place a negative over it and place 
the paper in the light  preferably strong sunlight in such a way that the 
negative is held flat to the paper and is unable to move. A contact 
printing frame is usual, but a spare or old photograph frame will do. 
Watch the paper darken where the negative is light. As soon as the paper 
has darkened in the areas where the negative is lightest ( to a level 
about as dark as the darkest area of the negative, remove the setup from 
the light and now we have to remove the paper from the frame and fix the 
image. This is done with hypo  a solution of thiosulphate  ammonium or 
even sodium will do. Put the solution in a tray big enough for the print, 
immerse the print, and leave it for a good while. Finally remove the 
print, wash it in running water for a while and hang up to dry. 
By the way, if the original was a print, you might be able to do the same 
thing and get a negative copy, but you would have to leave it in strong 
light for a long time. Only experimentation will tell you how long. If you 
can do that, you can then reverse the process to get back a positive 
image. Phew!

Good luck, and if my attempt answer your question has missed the mark, let 
me know either by direct e-mail, (harry.adam@btintermet.com) or by asking 
another MadSci question  with more background information.



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