Carbon transfer prints are a historic and intricate photographic printing process that was widely used in the late 19th and early 20th centuries. The process involves transferring a photographic image from a glass plate negative onto a paper support using carbon pigments. Carbon transfer prints are known for their exceptional image quality, permanence, and fine detail. It is estimated that fewer than 200 prints exist in the world.

Here's an overview of the carbon transfer printing process:

1. Creating the Negative: The process starts with the creation of a glass plate negative. This negative is made by coating a glass plate with a light-sensitive emulsion and exposing it to the original photographic image. The negative is then developed, resulting in a reversed image.

2. Preparing the Pigment Tissue: A sheet of thin tissue paper is coated with a mixture of gelatin and pigment. The choice of pigment can influence the tonal characteristics and color of the final print. Carbon black pigments were commonly used, but other colors could be used for special effects.

3. Sensitizing the Tissue: The coated tissue is sensitized with a solution that makes it receptive to the image from the glass plate negative.

4. Printing: The sensitized tissue is carefully placed in contact with the glass plate negative and exposed to light. The light penetrates the clear areas of the negative, hardening the gelatin in the tissue paper accordingly.

5. Development: After exposure, the tissue is washed to remove the unpolymerized gelatin, leaving behind a relief image created by the hardened gelatin. This is the carbon transfer relief print.

6. Transferring to the Final Support: The relief image is then transferred to the final support paper. This is done by placing the relief image in contact with the paper and applying pressure. The gelatin in the relief image softens and adheres to the support paper.

7. Drying and Finishing: The print is carefully dried and can be further processed to enhance tonal qualities or add hand-coloring if desired.

Carbon transfer prints are known for their long-lasting quality, exceptional detail, and the ability to control the final image's tonal range and color. The process is highly labor-intensive and requires a high level of skill, making it less common in the modern era. Nevertheless, it remains a favorite among fine art photographers and collectors for its unique and timeless aesthetic.