Silver bath maintenance for collodion wetplates part 1

This is the first part of my blog series for silver bath maintenance. In this part, the basics are described and focusses for beginning practitioners of collodion wetplate photography.


One of the key elements of wet collodion images is the silver bath. After coating a plate with collodion, it is dipped in a bath of a silver nitrate solution. Afterwards, a chemical reaction called “salt metathesis reaction“ takes place. In easy words, salts in the collodion solution (like ammonium iodine) combines with the silver nitrate to silver iodine and ammonium nitrate. Within minutes (2-3 minutes depending on the temperature) the reaction is completed. After that, the collodion wet plate is sensitive to light due to the presence of silver iodines and silver bromides.

When working with silver nitrate and its solutions, be aware that silver nitrate is the strongest oxidizer known, wear gloves and safety googles. If silver nitrate solution comes in contact with organic substances like your skin, it darkens everything and stains your clothes. Specifically, it can also blind you if you get a drop of it into your eyes. 

Always handle this chemical with the utmost respect!

Silver bath maintenance is a very important part of collodion wetplate photography and should be executed on a regular basis. A well maintained silver bath holds for many years, a very important point especially regarding silver nitrate prices nowadays.

a 11×14” tintype after sensitizing looks milky and is ready for exposure

Mixing the first silver bath

Most of the times, a 9% solution of silver nitrate is used for wetplate collodion processes. This means, that in every 100ml of distilled water, 9g of silver nitrate is added. Only use the finest grade 99.9% for your silver bath. This avoids impurities caused by other metals in the silver nitrate. 

As soon as you are getting into wet plate, you will find yourself in need to mix a new silver bath. Here is what you need:

  • 99.9% pure silver nitrate crystals
  • distilled water (don’t use demineralized or tap water!)
  • fine grain scale
  • hydrometer to measure density of the silver bath
  • a thin and elongated laboratory measuring cup (glass)
  • a glass bottle to hold the volume of silver nitrate
silver bath maintenance: mixing the silver bath
silver nitrate crystals on a scale

Now, let’s continue to mix one liter of 9% silver nitrate solution. 

  1. in a glass bottle, fill 1 liter of distilled water
    It’s very important to use distilled water, tap water has way to much minerals that will instantly combine with the silver nitrate. You will get a milky liquid. If you are using a new batch or manufacturer of distilled water, test the water with a little amount (100ml, 9g AgNo3) first to check if the solution stays clear.
  2. On a fine grain scale, measure 90g of silver nitrate crystals with care. Don’t be hasty and take your time. If you get a crystal on your skin, wash it immediately with water. 
  3. Add the silver nitrate crystals to the distilled water, close the bottle and shake well to dissolve the crystals.
  4. Now, fill the measuring cup with the silver nitrate solution to check the gravity and therefore, the purity of your silver nitrate. (see below)
  5. Coat a plate with collodion and let it sit in the bath over night. This iodizes the silver bath to work, meaning it regulates the pH a bit and brings in free iodines into the silver bath. 
  6. The next day: photograph with your fresh silver bath

Checking the specific gravity

One of the tools that I use is a hydrometer to check the strength of my silver baths. It’s quite clear: every plate takes out some silver, lowering the resulting strength of the silver nitrate bath. 

Note: checking specific gravity has the best accuracy if you have an ether and alcohol free silver bath (I’ll explain that in a later episode…).

The hydrometer is a tool to measure specific gravities of liquids and we can use it for check if we still have the 9% solution present. The hydrometer should have a scale from 1.05 to 1.10 and is dipped into the silver nitrate solution to float on it. On the scale, you can then read the strength.

Our target strength is a 9% solution, so the hydrometer will read 1.07, if it is lower, then you need to add silver, if it’s above, then add distilled water.

silver bath maintenance: checking specific gravity
checking specific gravity of your silver nitrate solution: the scale reads 1.07, so it is perfectly balanced to 9%

pH or not pH: silver bath maintenance

There are many confusions about the pH of your silver nitrate bath. Byproducts of your reaction of collodion salts and silver nitrate will lower the pH of your bath over the time. You can test your bath with a litmus strip very easily, be aware that electronic devices don’t work well because of the silver in the bath. 

The optimal pH range is from 3-4 for a workable bath, if your bath is more acid or less acid than that, you should do something, but nothing special: just sun your bath. 

All about light silver bath maintenance will be covered in the next episode of this blog.

For workshop dates, please visit this site.