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相纸也称照相纸、晒相纸、感光纸指覆以化学感光材料用以印制相片的特殊纸张。用以印制数码照相机的相纸不含化学感光材料成为印相纸。

Photographic Paper may be exposed to light in a controlled manner either by placing a negative in contact with the paper directly (contact printing) or by using an 放大机 to create 潜像. 然后相纸被显影化学品冲洗得到可见的像。

[编辑] 简史

自从1824年法国尼埃普斯和1841年英国威廉·亨利·福克斯·塔尔博特发明摄影术后，相纸的应用就开始了。时至今日相纸的应用十分普遍。

[编辑] 照相纸种类

I. Papers used for negative-positive photographic processes. (e.g. the Gelatin-silver process). This is the most common form of analogue photography. Even though slide film produces a positive image of a positive scene, the common process for the development of photographic transparencies (E-6) is actually a positive-negative process applied twice.

II. Papers used for positive-positive photographic processes in which the "film" is the same as the final image (e.g. the Polaroid process).

III. Papers used for positive-positive film-to-paper photographic processes in which a positive image is enlarged and copied onto a photographic paper (e.g. the Cibachrome process).

[编辑] I. Papers used for Negative-Positive Processes

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Image:En:Image:Photopapers 1.jpg

[编辑] 基本构造

相纸分四至五层:

纸基的基础是符合一顶质量标准的纤维纸基。相纸纸基必须颜色洁白、质地均匀、不易变形。纸基有不同的厚度标准。
氧化钡层。相纸纸基上加以薄层氧化钡，用以填充相纸纸基的小缺陷，增加相纸的洁白度。

相纸Photographic Papers are made up mainly of a Paper Base which can have a number of different surface characteristics. 常见的种类包括光面，亚光和绒面（麻面）. Specialised papers with unusual surface characteristics such as watercolour paper are also produced commercially (e.g. Kentmere's Art Document). If the printer produces his/her own Photographic Paper, any paper surface that permits the application of Photographic Emulsion is available. The thickness of the Paper Base is specified by its "weight" (single, double or triple weights are available).

有树脂层的相纸在氧化钡层上多加聚乙烯树脂层，用以阻止冲洗相纸时化学液体进入纸基。没有聚乙烯树脂层的相纸称为纸基相纸，具有聚乙烯树脂层的相纸称为涂塑相纸。

感光乳剂层

Even though different photographic processes use different chemical mixtures to record the exposure of the paper(s) to light, all Photographic Papers use a sensitised metal as a reactant to the exposure of light suspended in gelatin which is called the photographic emulsion. The metal is usually silver, but alternative processes exist that use iron (Cyanotype), platinum or palladium (Platinotype), uranium (Uranotype), or other metals. Photographic Emulsion can be sensitised for any wavelengths of light. In traditional black-and-white Photographic Papers, the Photographic Emulsion is only sensitised for blue light which allows processing under red/orange safelighting.

相纸表面保护层。

[编辑] 黑白相纸

[编辑] 纸基相纸(FB)

纸基相纸(2)包括一层纸基，有事上覆一层氧化钡以增加相纸的反射率使其更白，感光乳剂涂布其上。因感光乳剂吸水即膨胀变软，在冲洗过程中易受损伤，部分纸基纸在乳剂层上另涂一层透明的凝胶以保护乳剂。

Fibre-based papers are mainly used for exclusively high-quality prints and to maximise Archival Stability.

[编辑] 涂塑相纸 (RC)

The Paper Base of Resin-coated Photographic Papers (4) is sealed against the chemicals used for processing the paper by two polyethylene layers. Since no chemicals and no water is soaked into the Paper Base the time needed for processing, washing and drying of the paper is significantly shorter than the time needed for Fibre-based papers. In a traditional black-and-white darkroom, an RC print can be finished and dried within 10-15 mins. whereas the washing time of an FB print alone may take up to 60 mins.

大部分涂塑相纸都有乳剂保护层

[编辑] 彩色相纸

All color photographic materials available today are coated on either RC (resin coated) paper or on solid polyester. The photographic emulsion used for color photographic materials consists of three color emulsion layers (Cyan, Yellow and Magenta) along with other supporting layers. The color layers are sensitized to their corresponding colors.

The emulsion layers include the color dyes (Ilfochrome) or "color couplers" which react with color developers to produce color dyes (Type C prints).

[编辑] 感光膜特性

Photographic Papers are further distinguished by the characteristics inherent in their different Photographic Emulsions. Black-and-white Photographic Paper is available in different grades which are numbered 0 to 5, with 0 being the softest, or least contrastful paper grade and 5 being the hardest, or most contrastful paper grade.

Photographic Emulsions are also produced in a variable contrast type which permits the selection of any grade between 00 and 5. Variable contrast Photographic Paper is actually coated with two layers, one of which is very low in contrast (0 or 00) and one of which is very hard (5). The low contrast layer is activated by green light, the high contrast layer by blue light. The use of filters activates each layer in different proportions, thereby creating all contrast grades from 0 (or 00) to 5.

The trade names of variable contrast Photographic Papers are Variocontrast (Tetenal), Multigrade (Ilford) and Polygrade (Kodak). Other companies usually designate variable contrast type papers with the words variable or polycontrast.

The contrast of Photographic Papers can also be controlled during processing or by the use of bleaches or toners.

[编辑] 相纸的长期保存

任何相纸的寿命都取决于存放环境和冲洗的完善程度。

Fibre-based black-and-white Photographic Paper that has been processed archivally (Archival Processing) is considered archivally "stable" and should last at least 70 years。涂塑相纸因其多层的构造，长期保存易因为不同层次的吸水和受热膨胀率不同造成乳剂层脱落，一般认为寿命不超过40年。个别特殊的图像工艺，在处理得当的前提下，因其固有的稳定性而比纸基纸具有更加的保存性，例如。