Exposing and Developing the Tissue

Expose and Develop

Exposing the Tissue.jpg

The Workflow

Because this must follow immediately afterward process of sensitising by exposure and development, it is important to have a clear idea of the workflow before you begin. Here they are in summary

  1. Prepare and set aside your negative
  2. Select and set aside the final support
  3. Sensitise the tissue and set a timer for the drying time.
  4. As the end of the drying time approaches, get the mating bath ready with squeegee or roller, gloves, paper towels and the supporting glass and weights.
  5. Expose the tissue
  6. Using the bath, mate the tissue to the support
  7. Using weights to press the two together – while waiting get the development bath ready and to temperature
  8. Start the development process with the support and tissue mated – when ready separate the two and continue the development of the photograph
  9. Use cold water to stop development
  10. Hang out to dry. Any clearing and finishing can be performed after the print has dried

In this blog I am taking steps 5 to 9 - the previous steps my blog about Sensitising the Tissue



  • Tap water for development at 50 Celcius

Photographic Items

  • Negative pre-prepared and ready
  • Tissue, cut to size and sensitised
  • Support, cut to size and ready


  • Light box for exposure
  • Thin sheet (0.07mm) to protest negative - not used initially
  • Mating bath (18 Celcius)
  • Development bath (45 Celcius)
  • Thermometer
  • Squeegee or roller
  • Gloves
  • Large roll of paper towel
  • Timer

Expose the Tissue

I use my own home-made UV light-box that has eight blacklight blue fluorescent tubes, which have a peak intensity at about 370nm - perfect for the sensitised tissue, which maximum sensitivity in the range 350-420 nm.

With gum printing I found that 7 minutes works well. However, I establish the appropriate exposure time by placing the clear piece of colour separation film that I use for all my negatives and expose it in 1 minute increments up to 10 minutes. I will then select the minimum time to achieve full exposure, which I will discover by developing the exposed test piece

I don't use a contact printing frame, instead I use a sheet of heavy plate glass with weights. You can see from the picture at the top of this blog that my weights are unusual (they are hip replacements that I have collected in my day job). It is recommended by by King and Lockhart to use a thin sheet of plastic to protect the negative. My plan is not to do so to begin with, but to do so it I find it necessary

The steps I am going to follow (once I have established the exposure time) is:

  1. Align the negative and the tissue carefully and apply the plate glass. I do this on an MDF tray before inserting into the light-box
  2. Once in the light-box apply the weights
  3. Select the time and start
  4. After exposure, remove from the light-box and separate and store the negative
  5. The tissue is ready for development

Mating the Tissue and Support

I am going to try the 'no-wait' mating technique - or a short variation of it from Sandy King. I will soak the support for four minutes and add the tissue after a minute so it is immersed for three minutes. I will use a developing bath that is 18 Celsius)

The steps I am going to follow are:

  1. Get the mating bath ready at 18 Celsius and the developing bath at 45 Celsius
  2. Drop and fully immerse the support starting the four-minute countdown
  3. Add and fully immerse the sensitised tissue after a minute
  4. Remove the support and the tissue at four minutes, align them jelly to sized support surface and squeegee or roller them together, making sure all the air has been expelled between them
  5. Separate the tissue and the support after five minutes
  6. Once separated keep the tissue to be cleaned and recycled and put the support into the developing bath
  7. With continuous side-to-side agitation the development should be ready in 6 to 10 minutes - check regularly on how it is developing and stop early if highlights clear
  8. The development it arrested by dropping the print into cold water
  9. Don't touch the delicate carbon tissue, but enjoy the image in relief when the tissue is wet
  10. Hang up to dry - steps may be need to prevent the print from curling

Lessons Learnt

  1. Even the part of the tissue that was unexposed was grey - clearly the tissue is more sensitive than the gum I am used to and needs to be prepared under a safe light
  2. The 'no-wait' mating technique was not successful and the jelly floated free before being fully developed
  3. There were clear steps in the tissue showing that it was responding to the UV - though it looks as though it is fully exposed in a few minutes