Trouble Shooting Tin
There's been a lot of chatter out there over the years about image artifacts that appear on tin. The simplistic response is to blame the tin, but this, in fact, is only a small part of the story, because the same general failure mode can also be made to occur on glass.
What are the factors responsible for these noisy shadow areas, spots and streaks? The truth of the matter is that the artifacts traditionally blamed on tin are in fact the result of either excessive development times, the use of improperly ripened collodion, or a combination of both. It's important to realize that tin related artifacts do not occur in isolation.
So what can be done to make these artifacts vanish?
First, avoid excessively long development times. In the experiments we've conducted, 15 seconds of development using a 5% ferrous sulfate developer works well. Monitor development time using a metronome for consistency. Stop development at the completion of the development time regardless of what you see on the plate. If the resulting image density is inappropriate, correct this through exposure, not by altering development times.
Secondly, insure that your collodion has been properly ripened before using it. As collodion ages, small amounts of iodine are released into solution. This produces the characteristic amber color we're all familiar with. It also increases the acidity of the collodion, improving it's resistance to fogging and other artifacts. This ripening time varies depending on the formula used and even upon the age of the ether used to make the collodion. A reasonable average for ripening is approxiamtely 3 weeks. If you intend to use collodion that's insufficiently ripened, the process can be artificially accelerated by adding tincture of iodine to the collodion at the rate of 3 to 4 drops per 30 millileters (1 ounce). More can be added if necessary.
By paying attention to these two factors, the often mischaracterized "tin artifact" can easily be made to vanish.
|An example of some of the ugliest tin I could find - tin that you might be afraid to even try. The sheet on the left has the plastic coating in place, while the sheet on the right has the plastic coating removed. My goal here is to show you that spots and streaks that are often attributed to the tin are actually caused by improper development and exposure. Even this ugly tin can produce exceptional images.
To illustrate the effect of exposure and development on spots and streaks in the image, consider the photo to the left. The left most of the image is clean, with clear blacks in the background. By contrast, the black background of the right half is obscured with spots and streaks.
“So what could possibly cause such a dramatic difference in the images?”, you might be asking yourself (and if you’re not, you should be!).
The difference here lies in the development time. The image on the left was given a 20sec exposure with 15 seconds of development while the image on the right had a 5 second exposure with 40 seconds of development using a 5% ferrous sulfate developer. All other variables were held constant.
This comparision illustrates the relationship between unripened collodion and spots and streaks in the image. The image on the left was made using newly mixed collodion that had not been allowed to ripen sufficiently. The image on the right was made using the same collodion and the same tin, but 4 drops tincture of iodine was added per ounce of collodion to artificially acelerate the ripening process.
The proper ripening of collodion has a significant effect on preventing so called "tin artifacts".
|Various formulas were mixed and allowed to ripen over time. As the ripening process progresses, the color of the collodion gradually darkens as free iodine begins to accumulate in solution. 3 weeks appears to be a reasonable average for a sufficient ripening time. If collodion needs to be used before it has properly ripened, the process can be accelerated artificially by adding tincture of iodine.