Historical Context

Carbon printing was developed in the 1850s-60s, with Joseph Swan patenting a practical commercial process in 1864. Carbon prints are among the most permanent photographs possible—the image is composed of pigmented gelatin rather than metallic silver, and properly made carbon prints can last for centuries.

Process Overview

Carbon printing involves creating "tissue" (pigmented gelatin on a temporary support), sensitising it with dichromate, exposing through a negative, transferring to a final support, and developing in warm water to dissolve unhardened gelatin.

Chemistry

Carbon Tissue Formula (basic recipe)

Component	Amount
Gelatin (photographic grade)	50 g
Pigment (lampblack, iron oxide, etc.)	As needed
Sugar	10-15 g
Glycerol (optional plasticiser)	5 ml
Distilled water	500 ml

Preparation

Soak gelatin in cold water for 30 minutes
Heat gently to dissolve (do not boil)
Add pigment (pre-dispersed in water), sugar, and glycerol
Pour onto temporary support (conditioned paper or plastic sheet)
Allow to dry flat (24-48 hours)

Sensitiser

Component	Amount
Potassium dichromate or ammonium dichromate	20-50 g
Distilled water	1 litre

Higher dichromate concentration = higher contrast.

Procedure (Single Transfer)

Sensitise tissue: Under subdued tungsten light, float dried tissue face-down on sensitiser for 2-3 minutes. Hang to dry in darkness.
Exposure: Contact print sensitised tissue under UV light, tissue emulsion facing light, with negative placed emulsion-to-emulsion.
Mating: After exposure, soak tissue in cold water until limp. Press tissue firmly onto final support (paper or other substrate), squeegee to ensure contact.
Development: After mating, place sandwich in warm water (38-42°C). The temporary support will separate. Gently agitate in warm water—unhardened gelatin dissolves, leaving the image.
Clearing and drying: Allow print to cool, clear in alum bath if desired, wash, and dry.

Single vs Double Transfer

Single Transfer

Tissue transfers directly to final support
Image appears reversed (laterally flipped)
Produces maximum relief effect
Simpler process

Double Transfer

Tissue transfers to temporary support first, then to final support
Corrects image orientation
Allows use of textured final papers
More complex but more flexible

Making Your Own Tissue

While commercial carbon tissue is available, many practitioners make their own:

Choose pigment: Lampblack for neutral tones, iron oxides for warm tones, or any lightfast pigment
Disperse pigment: Grind pigment with a small amount of water to form paste
Mix with gelatin: Add dispersed pigment to warm gelatin solution
Pour and dry: Pour onto release layer (typically conditioned paper) and dry flat

The ratio of pigment to gelatin affects both the colour density and the printing characteristics of the tissue.

Troubleshooting

Problem	Likely Cause	Solution
Image too light	Underexposure; overdevelopment	Increase exposure; lower water temperature
Image too dark	Overexposure; underdevelopment	Decrease exposure; raise water temperature
Frilling (edges lifting)	Poor tissue/support adhesion	Better mating; ensure good contact
Mottle	Uneven sensitisation or development	Improve technique; consistent agitation

Safety

Chemical	Hazard	Precautions
Potassium/ammonium dichromate	Carcinogenic; toxic; skin sensitiser	Gloves essential; ventilation; avoid skin contact; proper disposal required

Hexavalent Chromium Warning

Dichromates contain hexavalent chromium (Cr VI), which is carcinogenic and can cause severe skin sensitisation. EU regulations have restricted amateur use of dichromates since September 2017.

Always:

Wear nitrile gloves
Work in well-ventilated areas
Avoid skin contact—chromium sensitisation can be permanent
Dispose of waste according to local hazardous waste regulations
Consider alternative sensitisers where available

Carbon Transfer

Image characteristics

Key chemicals