Wet Plate Collodion - Silver Bath Gravity Maintenance

Dear World,

I'm relatively new to the world of Wet Plate Collodion, however I have been shooting almost daily for the last couple of months.

As I have never had to do it before, my question is;

- How exactly do you maintain the gravity of your silver nitrate bath?

I started with a 400ml 9% bath (36grams of silver in 400ml of distilled water), which had a specific gravity of 76

I now I have 370ml bath at a specific gravity of 62

I'm really noticing the loss of good contrast and true blacks in my images, so I would like to fix this as soon as possible.

Side notes:
- I have been sporadically filtering my bath threw proper laboratory filter paper
- I am familiar with 'sunning' the silver bath, but I am yet to do so.

Any info anyone could give me would be greatly appreciated!!

Thank you kindly,
Matt

Matt, you will need to get your silver levels back up by adding in silver nitrate crystals to get the same specific gravity you had initially. Thats only half the story though. While it should work, just be aware that during the sensitizing process, your halides will enter into the silver bath during the molecular exchange of silver onto the plate. These iodide compounds will fall into the silver bath and over time will add up to the point where they impact your SG readings making you think that you have enough silver content in your bath when in all actuality, you do not. Normally sunning and filtering takes care of most issues, and replenishing with silver to get the bath back to normal. At some point, these iodides can increase to a point where you have an over iodized bath. This will require a neutralizing step by adding ammonium hydroxide to bring ph down to 7. Then, after a lot of sunning, most of this will precipitate out to the bottom (more so than with regular sunning). Then filter as normal. What many people do after this step is to heat the silver nitrate and reduce the liquid volume down till its almost gone, then rehydrate with fresh distilled water. This will remove the alcohol smell in the silver bath, and help developer pours etc like its a new silver bath. After re-hydrating, add silver nitrate crystals to get back to normal SG. Then add nitric acid to get the ph back to around 4. Your bath will then be like its brand new. Doing these additional maintenance steps means your silver bath will last indefinitely with careful scheduling. I myself keep 3 x 1 liter baths in a rotation. Where one is the working bath, one is the backup, and one is having some type of maintenance... I would als join the collodion.com forum ran by Quinn Jacobson, there is a ton of data on there that might be of use.

Specific gravity of 76, are you speaking of neutronium? Let's get our terminology straight. You mean a specific gravity of 1.076. The correct range is 1.065 to 1.080. Therefore if the specific gravilty is too low you just add a bit more silver nitrate.

I don't pay much attention to the specific gravity of the silver bath. After it has been used for awhile, I think you'd have to do a titration to get an accurate measure of the silver concentration.

As soon as the silver bath is used, silver is being taken out of the bath but other metal cations such as cadmium and potassium exchange into the mix. Lighter stuff like diethyl ether and ethanol are being introduced and iodides and bromides are also reacting with it to some extent. With all that going on I don't think a simple hydrometer test is going to be a reliable indicator of silver content except when the bath is first mixed. But, you really don't need it at that step either (unless you have faith in its accuracy later on) because you know the percent solution being mixed and the amount of silver nitrate needed to get it there.

After running some plates through the bath I occasionally bring the volume back to the starting point by adding some higher concentration solution to the main bath. Every once in awhile I sun the bath before I start having problems with it and like Andrew, I also have a backup bath or two. Sunning the bath gets rid of the organics and also allows the ether and alcohol to evaporate.

If you have lost 30ml of your bath (7.5% of the original volume) add 30ml of a more concentrated solution of silver nitrate to compensate. Most use a 30% solution of silver nitrate to replenish. (Kodak recommended a 10% solution to replenish a 7.5% original bath.) Even if you are off a bit by using this method, it probably creates an error no larger than what the hydrometer will tell you. (That's an assumption on my part.) If your silver bath becomes too strong as a result, just add some distilled water.

Instead of messing with the silver bath chemically, I think you should direct your concern to keeping everything clean, filtering daily, and sunning the bath every once in awhile. John Coffer discusses that sentiment in his Mythbusters series.

The following attachments are scans I made of a few pages of Kodak's booklet on wetplate collodion concerning silver bath maintenance. Use of a hydrometer is discussed as well as the procedure for correcting an over-iodized bath (as Andrew has alluded to previously).

Thanks for the info guys! Its a big help. Its hard when your sitting here and have no one to easily call up and ask in real life.
Andrew - Thanks for the detailed info and advice, and I'm scouring the collodion.org forums now.
Gerald, yes sorry. I meant 1.076, my hydrometer abbreviates the reading.
Smiegliitz, thanks alot for going to the trouble of the scan! and your advice.

Hopefully between all of the above I can start to get this silver bath sorted!

Cheers,
Matt

Sunning the bath and establishing the strength of the Silver Solution

Here is our experience with servicing silver baths over the years

No amount of filtering will remove the finest organic matter, nitrates and free iodides from a silver solution use in the wet plate process. Organic matter in the bath is one of the main causes of veiling on collodion plates. The other being impure or not properly filtered developer.

The silver solution will also contain acid, alcohol and ether after use. Sunning the solution in a large clear open container will remove the alcohol and ether by evaporation. Sunning works best if you bring up the pH a little toward the neutral side with bicarb before sunning. Sunning is the only effective way to remove all fine organic matter. It will not remove free iodides however. The solution requires the addition of more water and a boiling treatment for that, but if you are making tintypes or ambrotypes...you will not generally see the pinholes caused by free iodides. Negative making requires more "nicety" than positive making as a general rule and as you'll notice most people are making tintypes and ambrotypes these days.

Once sunned, so that the silver solution first turns dark and then clear again, you may filter the solution and test with a hydrometer to get a good enough test to show if you need to add water or silver to bring it up to the specs of a newly made silver solution. We never take note of the scales...just mark the shaft at the starting level with a sharpie as your bench mark.

The main thing to remember is that testing a used silver bath without sunning it first [to remove the alcohol and ether] shows you absolutely nothing..since hydrometers also measure the specific gravity of alcohol and ether. Very few wet plate photographers used titration in the 19th century, but a whole lot of them used hydrometers.

By the way, when we first came on the scene in the late 1980s...those few who were also doing wet plate, retired their silver baths completely when they showed signs of problems. Despite what they may tell you now..they stored gallons of them in back rooms and outdoor sheds. We have been using elements of our first bath since the very beginning and have always thought sunning was the best thing you could do to an over worked bath. We always test a sunned bath with a hydrometer...and strangely, have been able to make some pretty good images over the years, both positive and negative. ;-)

I am starting up my first silver nitrate bath 9% and wonder, approximately, how many 4x5 plates I can sensitize in a 250ml bath tank before the silver content goes too low that it effect the quality of the wet plate image?