![]() ![]() However, if dichromate must be used for a specific unavoidable reason, a gelatin with a low pH will be more susceptible to the dark reaction due to the build up of chromic acid, leading to prints that come out too dark. That being said, usually the higher bloom gelatins are cleaner, and reserved as photographic or pharmaceutical grade by gelatin manufacturers, and tend to be more expensive.Ī gelatin’s pH is only important when working with dichromate as the sensitizer, which I strongly discourage for many reasons. The stronger gelatins take longer to bloom before melting and need a longer soak in the mating bath, but that’s about the only difference I’ve observed. There might be a slight correlation between contrast and bloom, but it’s a stretch since the 60 bloom gelatin has the same contrast as some of the 290 bloom gelatins. In the strip of tests at the top of this page, there are samples of gelatin ranging from 60 bloom to over 300 bloom, and they all work just fine. Adding a bit of a biocide will prevent this, but using a gelatin that has a very low amount of bacteria to start off with will help and limit the amount of biocide needed. When poured the emulsion looks perfect, but when you come back in the morning, the emulsion is covered with small bubbles. A crystal-clear gelatin will give a nice clean look to a print, and the coating won’t be noticeable.īelow is a photograph of what happens when bacteria start to grow in an emulsion while it is drying. A yellow gelatin will create a yellow paper when coated. The variation of density between the various gelatin samples was minimal, so even a brownish gelatin is fine for black and white work.įor coating paper, clarity is by far the most important aspect to look at. To see if that has an effect on densities, I did a test by exposing patches of a single emulsion through 100 micron thick layers of dry gelatin. On technical data sheets of gelatin samples the UV and visible transmission is usually indicated. A clear gelatin will allow for brighter colors in a print. When making color prints, using a yellowish gelatin will cause blues, turquoises, and cyans in the print to come out muddy. The numbers in blue marker are the change in density. The green square is best, while the black squares are going to make calibration a major headache. Below are some examples of stable and unstable samples of gelatin. Getting the correct exposure is like trying to hit a moving target. Imagine shooting with ISO 100 film in January, but when you come back to use the film in June it has changed to ISO 200. Some types of gelatin will cause an emulsion to change speed over time. A good middle of the road gelatin is going to be the best for most prints. Likewise, use a gelatin that is too low in contrast, and exposure times become ridiculously long. ![]() Use a gelatin that’s too high in contrast, and you will find that creating accurate tonal separations becomes an almost impossible task. The variation in contrast between the strips is quite remarkable. In the test strips above, all tests were made with the same amount of pigment and sensitizer and exposed at the same time. This oversight can lead to frustration in getting clean highlights in a print, and deep rich blacks. ![]() There are many ways to change the contrast of an emulsion, but changing the gelatin is often overlooked. Instead of looking like the print on the left below with clean whites, if a staining gelatin is used then the print will look like the one on the right below. In the photo above you will see the middle gelatin caused the pigment to stain the paper. In order of most important to least important, here are the things to look for in a quality gelatin for carbon printing. “What bloom gelatin to you use?” That’s the first and usually only thing I ever get asked about gelatin, but it also happens to be one of the least important aspects in choosing a quality gelatin for carbon printing. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |