Notes on Salt Printing

Don't make salt prints with unsized paper.

Always size the paper before coating with the salt solution.

To size the paper weigh 2g of gelatine and mix in circa 30ml of water. Make sure it is dissolved and leave it for 10 minutes until the sizing solution blooms. Heat 70ml of water to circa 50°C and then mixing it in to the 30ml of gelatine solution you already prepared to make 100ml. Allow to cool a little. The sizing solution is best applied at about 40°C. A hotplate and magnetic stirrer is very useful for making a sizing solution. The solution once cooled can be kept in the fridge for later use but it will go hard so you'll need to warm it again for further sizing.

When using a brush and certainly a foam brush to apply any coat of solution make sure it is damp otherwise you'll think you have coated the paper evenly when you haven't. 

See Image below:

I have made this mistake on many occasions and it's very frustrating if you have prepared 10 sheets of paper incorrectly. Unfortunately you will not know you have made this mistake until you start exposing the paper and notice patches of unexposed areas. 

Once you have sized the paper with your 2% gelatine solution and allowed it to completely dry it is time to coat your paper with a 2% NaCl (sodium chloride) solution. Not any salt will do. Make sure your salt is free from addatives like caking agents and Iodine. I use 'pharma grade' Sodium Chloride.

Simply mix 2g of salt into 100ml of distilled water until it dissolves. This can be done at room temp. 

To apply the salted solution to the sized paper pour circa 3ml into a saucer and with a damp brush apply the solution going across the paper and along the paper until you are sure the paper is completely covered. The paper will now need to dry for about 1 hour. 

Once the paper is completely dried it is time to apply the 12% Silver Nitrate and 6% Citric Acid solutions.

With a syringe or pipette dispense about 2ml of the 12% Silver Nitrate solution and about 2ml of the 6% Citric Acid solution into a small glass container (a shot glass will do). Mix it together with a glass rod or plastic spoon (not metal as it will react with the Silver Nitrate). Pour the mixed solution into the middle of the sheet paper and brush the liquid from the middle in both vertical and horizontal strokes, making sure your brush is slightly damp to avoid streaks and areas misssed by the sensitizer. Make sure the area you are going to be exposing with your digital negative or photogram is completely and evenly covered with the combined solution.

Allow to dry for about 1hr. 

It's now time to expose the the paper. Exposure time very considerably depending on UV index if exposing by sunlight or whether you are using a UV Exposure unit (most salt prints I make are about 8-10min with a UV Exposure Unit. 

Sandwich a relatively high contrast digital negative between a weighted sheet of glass and the sensitized paper and expose. If you are uising a contact frame you can check the exposure of the image by liofting up one half of the frame without deregistering the negative. The image should appear about 1 or 2 stops darker than you would like it as it will lose a little in the wash and fix.

Once Exposed it's time to wash and fix.

You will need two trays. One for just water and one for the fixer. You'll notice when you initially wash the print the unexposed silver will come off the image and make the water slightly cloudy. You need to wash the image until you cannot see anymore cloudyness in the water. Replace the water 2 or three times in the tray until it runs clear. A wash of about 3 -4 mins should be sufficient.

Once washed transfer to a already made up bath of of 10% Sodium Thiosulphate (Hypo) solution and fix for about 5 minutes with occasional agitation. Once fixed re-wash the print for about 15min under running water or 5 / 6 water bath changes if you are in the mood to conserve. 

To print can now be hung up to dry.

Happy printing.