To make paper light sensitive, you coat it with materials that react to light, undergoing a chemical or physical change when exposed. This allows the paper to record an image when specific areas are exposed to light and others are not.
The Basics of Light-Sensitive Paper
Light-sensitive paper, often called photographic paper, is fundamental to many historical and alternative photographic processes. Its sensitivity comes from applying an emulsion or coating containing light-reactive compounds, usually silver salts for traditional photography, or other chemicals like iron salts for processes like cyanotype, or even natural plant pigments.
When light hits these compounds, it initiates a chemical reaction that creates a latent image. This image is then "developed" and "fixed" using further chemical baths, revealing a permanent visible image.
Traditional Chemical Methods
Several established chemical processes allow you to transform ordinary paper into light-sensitive material. These methods are at the heart of historical photography and alternative printing.
Cyanotype Process (Blueprints)
The cyanotype process, known for its distinctive Prussian blue prints, is one of the easiest and safest ways to make paper light sensitive. It involves two main chemicals that react to UV light.
Ingredients:
- Solution A: Ferric Ammonium Citrate (green variety)
- Solution B: Potassium Ferricyanide
- Distilled water
- Paper (watercolor or art paper works best)
Steps to Make Cyanotype Paper:
- Prepare Solutions: Dissolve equal parts (by weight) of ferric ammonium citrate in water to make Solution A, and potassium ferricyanide in water to make Solution B. Store them separately in dark bottles.
- Mix Emulsion: In a dim or low-light environment (avoiding UV light), mix equal parts of Solution A and Solution B. This mixture is now light sensitive.
- Coat Paper: Using a brush, sponge, or coating rod, apply an even layer of the mixed solution onto your chosen paper.
- Dry in the Dark: Hang the coated paper in a dark, dust-free area to dry completely. Once dry, it's ready for exposure.
- Expose: Place objects or a photographic negative on the dry paper and expose it to UV light (sunlight or a UV lamp).
- Wash: After exposure, wash the paper thoroughly in running water to remove unexposed chemicals, revealing the blue image.
- Dry: Allow the finished print to air dry.
For more detailed instructions, you can refer to resources like The George Eastman Museum's Cyanotype Process guide.
Salted Paper Prints
One of the earliest photographic processes, salted paper prints use silver chloride embedded in the paper fibers.
Ingredients:
- Salting Solution: Sodium chloride (table salt) dissolved in water.
- Sensitizing Solution: Silver nitrate dissolved in water.
- Paper (often cotton-rag paper).
Process Overview:
- Salt the Paper: Paper is first soaked in a solution of salt, which impregnates the fibers with chloride ions.
- Sensitize: Once dry, the paper is coated in a darkroom with a silver nitrate solution. The silver nitrate reacts with the chloride ions to form light-sensitive silver chloride within the paper.
- Dry and Expose: The paper is dried in the dark and then exposed to UV light under a negative.
- Process: After exposure, the print is washed, toned (often with gold chloride for permanence and color), and fixed using a thiosulfate solution to make the image permanent.
Silver Gelatin Emulsion
This is the most common method for modern black-and-white photographic papers. It involves suspending microscopic silver halide crystals (like silver bromide or silver chloride) in a gelatin binder.
Characteristics:
- High Sensitivity: Allows for very fast exposure times.
- Detail: Capable of capturing fine detail and a wide range of tones.
- Complex Production: While commercially available, preparing silver gelatin emulsions from scratch is a highly complex process usually undertaken in specialized darkroom environments due to the precision and safety requirements involved.
DIY and Natural Approaches
Beyond chemical solutions, you can also explore natural methods to create light-sensitive paper, albeit with different results and sensitivities.
Plant-Based Pigments (Anthotypes)
A unique and eco-friendly way to make paper light sensitive is by using the pigments extracted from plants. This method produces prints known as anthotypes, which are sensitive to UV light and typically fade over time rather than being permanent.
How to Make Paper Light Sensitive with Plants:
You can make your own light-sensitive paper by extracting coloured juices from plants and coating paper. Plants rich in pigments, such as spinach, brassicas, rocket, wild garlic, beetroot, and coloured fruit, work well. You can also try experimenting with turmeric or flower petals for different color reactions.
Practical Steps:
- Extract Pigments: Crush or blend the plant material (e.g., spinach leaves, beetroot chunks, flower petals) with a small amount of alcohol (like rubbing alcohol or vodka) or water. Strain the mixture to get a concentrated liquid extract.
- Coat Paper: Apply the extracted coloured juice evenly onto paper. Watercolor paper or thick drawing paper works well.
- Dry in the Dark: Allow the coated paper to dry completely in a dark, well-ventilated area.
- Expose: Place opaque objects (like leaves or small trinkets) or a photographic negative onto the dry, coated paper. Expose it to strong sunlight for several hours or even days, depending on the plant and light intensity. The light will bleach the exposed areas, leaving the unexposed areas (under the objects) in their original color.
- Finish: Once the desired image is formed, simply remove the objects. No further chemical processing is needed, but anthotypes will continue to fade if exposed to light.
Key Considerations for Making Light-Sensitive Paper
| Aspect | Description |
|---|---|
| Paper Choice | Use high-quality paper (e.g., watercolor paper, cotton-rag paper) that can withstand wetting and has a good surface for coating. Avoid papers with optical brightening agents. |
| Coating | Apply coatings evenly and without streaks for consistent results. Multiple thin coats are often better than one thick coat. |
| Drying | All light-sensitive papers must be dried completely in the dark, away from any light source, including UV from fluorescent bulbs. |
| Safety | When working with chemicals like silver nitrate or potassium ferricyanide, always wear gloves and eye protection and work in a well-ventilated area. Dispose of chemicals responsibly. |
| Light Source | Most alternative processes (cyanotype, anthotype, salted paper) are primarily sensitive to UV light, making sunlight an excellent and free exposure source. |
| Storage | Unexposed light-sensitive paper should be stored in light-tight containers or bags, ideally in a cool, dry place, to maintain its sensitivity and prevent premature fogging. |
By understanding these methods, you can explore the fascinating world of creating your own light-sensitive paper for unique photographic and artistic expressions.
