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  1. #1
    htmlguru4242's Avatar
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    Dichromate on Paper - hmm

    To test the question I posed eariler about sodium dichromate being light sensitive, I coated some of my tray cleaner with a brush onto paper, let it dry, and put it out into the sun (errr, what little there is on a slighlty cloudy day with snow all over). Within about a half hour, it turned from its yellow - orange color to a nice deep brownish - red - orange. (A section underneath a piece of foil remained unchanged). Wala- light sensitive.

    Trying it again with a negative didn't work too well as my highest - contrast stuff is still a bit lacking for it (and a bit too small, probably, as its all 120 stuff - all the 4x5 negs. are not as good).

    The image resulting after 50 minutes was very low contrast on the page, but the clearest areas of the negative were visible as dark patches on the paper. The rest of the detail did not come out so well. I'm sure that more exposure could have helped.

    I'm going to play with this to see what I can do.

    I've thought of neutralizing the sulfuric acid in the tray cleaner with sodium hyrdoxide, though that leaves me with aqueous sodium sulfate (yes?) to deal with. So, I'll bite the bullet and it's off to Photo Formulary to buy some dichromate.

    Also to figure out what to do to kill the light sensitivity after exposure - precipitate it in the paper to some other chromium compound perhaps?

  2. #2
    Photo Engineer's Avatar
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    Quote Originally Posted by htmlguru4242
    To test the question I posed eariler about sodium dichromate being light sensitive, I coated some of my tray cleaner with a brush onto paper, let it dry, and put it out into the sun (errr, what little there is on a slighlty cloudy day with snow all over). Within about a half hour, it turned from its yellow - orange color to a nice deep brownish - red - orange. (A section underneath a piece of foil remained unchanged). Wala- light sensitive.

    Trying it again with a negative didn't work too well as my highest - contrast stuff is still a bit lacking for it (and a bit too small, probably, as its all 120 stuff - all the 4x5 negs. are not as good).

    The image resulting after 50 minutes was very low contrast on the page, but the clearest areas of the negative were visible as dark patches on the paper. The rest of the detail did not come out so well. I'm sure that more exposure could have helped.

    I'm going to play with this to see what I can do.

    I've thought of neutralizing the sulfuric acid in the tray cleaner with sodium hyrdoxide, though that leaves me with aqueous sodium sulfate (yes?) to deal with. So, I'll bite the bullet and it's off to Photo Formulary to buy some dichromate.

    Also to figure out what to do to kill the light sensitivity after exposure - precipitate it in the paper to some other chromium compound perhaps?
    Isn't this the gum bichromate process sometimes used to make decals?

    I have not been following the other thread, but it seems that I made decals this way many many years ago. It was also used for some silk screen work.

    PE

  3. #3
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    Quote Originally Posted by htmlguru4242
    To test the question I posed eariler about sodium dichromate being light sensitive, I coated some of my tray cleaner with a brush onto paper, let it dry, and put it out into the sun (errr, what little there is on a slighlty cloudy day with snow all over). Within about a half hour, it turned from its yellow - orange color to a nice deep brownish - red - orange. (A section underneath a piece of foil remained unchanged). Wala- light sensitive.

    Trying it again with a negative didn't work too well as my highest - contrast stuff is still a bit lacking for it (and a bit too small, probably, as its all 120 stuff - all the 4x5 negs. are not as good).

    The image resulting after 50 minutes was very low contrast on the page, but the clearest areas of the negative were visible as dark patches on the paper. The rest of the detail did not come out so well. I'm sure that more exposure could have helped.

    I'm going to play with this to see what I can do.

    I've thought of neutralizing the sulfuric acid in the tray cleaner with sodium hyrdoxide, though that leaves me with aqueous sodium sulfate (yes?) to deal with. So, I'll bite the bullet and it's off to Photo Formulary to buy some dichromate.

    Also to figure out what to do to kill the light sensitivity after exposure - precipitate it in the paper to some other chromium compound perhaps?
    You need an organic compund such as gum acacia to fix the image on to paper. Also without the addition of a pigment any image obtained is likely to be very faint. I'm not sure what you are aiming to achieve but in the end I'm sure it will be wondeful. Let us all know how it turns out.

    Don Bryant

  4. #4

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    Yes, sodium dichromate is interchangable with the ammonium dichromate or potassium dichromate used in gum printing, but it's more expensive and used much less than either of the other compounds.

  5. #5
    htmlguru4242's Avatar
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    Wold it be possible to convert the dichromate on the page to another compound, say, chromium hydroxide? I know that it's doable when neutralizing the stuff as a bleach to dispose of it ... perhaps this could be done on the paper, resulting in a blue - green image?

  6. #6

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    The dichromates work by hardening a colloid when exposed to light.

  7. #7
    htmlguru4242's Avatar
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    I do know that, NWorth, though what I'm talking about her eis the fact that they also turn dark in the sun.



 

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