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Photographic emulsion

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Title: Photographic emulsion  
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Subject: Photography, Photographic film, Pion, Holography, Anti-halation backing
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Photographic emulsion

Photographic emulsion is a light-sensitive colloid. Most commonly, in silver-gelatin photography it consists of silver halide crystals dispersed in gelatin. The emulsion is usually coated onto a substrate of glass, films of cellulose nitrate, cellulose acetate or polyester, paper or fabric.

Photographic emulsion is not a true emulsion, but a suspension of solid particles (silver halide) in a fluid (gelatin in solution). However, the word emulsion is customarily used in a photographic context. Gelatin or gum arabic layers sensitized with dichromate used in the dichromated colloid processes carbon and gum bichromate are sometimes called emulsions. Some processes do not have emulsions, such as platinum, cyanotype, salted paper, or kallitype.

Components

Photographic emulsion is a fine suspension of insoluble light-sensitive crystals in a colloid sol, usually consisting of gelatin. The light-sensitive component is one or a mixture of silver halides: silver bromide, chloride and iodide. The gelatin is used as a permeable binder, allowing processing agents (e.g., developer, fixer, toners, etc.) in aqueous solution to enter the colloid without dislodging the crystals. Other polymer macromolecules are often blended,require('Module:No globals')

local p = {}

-- articles in which traditional Chinese preceeds simplified Chinese local t1st = { ["228 Incident"] = true, ["Chinese calendar"] = true, ["Lippo Centre, Hong Kong"] = true, ["Republic of China"] = true, ["Republic of China at the 1924 Summer Olympics"] = true, ["Taiwan"] = true, ["Taiwan (island)"] = true, ["Taiwan Province"] = true, ["Wei Boyang"] = true, }

-- the labels for each part local labels = { ["c"] = "Chinese", ["s"] = "simplified Chinese", ["t"] = "traditional Chinese", ["p"] = "pinyin", ["tp"] = "Tongyong Pinyin", ["w"] = "Wade–Giles", ["j"] = "Jyutping", ["cy"] = "Cantonese Yale", ["poj"] = "Pe̍h-ōe-jī", ["zhu"] = "Zhuyin Fuhao", ["l"] = "literally", }

-- article titles for wikilinks for each part local wlinks = { ["c"] = "Chinese language", ["s"] = "simplified Chinese characters", ["t"] = "traditional Chinese characters", ["p"] = "pinyin", ["tp"] = "Tongyong Pinyin", ["w"] = "Wade–Giles", ["j"] = "Jyutping", ["cy"] = "Yale romanization of Cantonese", ["poj"] = "Pe̍h-ōe-jī", ["zhu"] = "Bopomofo", }

-- for those parts which are to be treated as languages their ISO code local ISOlang = { ["c"] = "zh", ["t"] = "zh-Hant", ["s"] = "zh-Hans", ["p"] = "zh-Latn-pinyin", ["tp"] = "zh-Latn", ["w"] = "zh-Latn-wadegile", ["j"] = "yue-jyutping", ["cy"] = "yue", ["poj"] = "hak", ["zhu"] = "zh-Bopo", }

local italic = { ["p"] = true, ["tp"] = true, ["w"] = true, ["j"] = true, ["cy"] = true, ["poj"] = true, } -- Categories for different kinds of Chinese text local cats = { ["c"] = "", ["s"] = "", ["t"] = "", }

function p.Zh(frame) -- load arguments module to simplify handling of args local getArgs = require('Module:Arguments').getArgs local args = getArgs(frame) return p._Zh(args) end function p._Zh(args) local uselinks = not (args["links"] == "no") -- whether to add links local uselabels = not (args["labels"] == "no") -- whether to have labels local capfirst = args["scase"] ~= nil

        local t1 = false -- whether traditional Chinese characters go first
        local j1 = false -- whether Cantonese Romanisations go first
        local testChar
        if (args["first"]) then
                 for testChar in mw.ustring.gmatch(args["first"], "%a+") do
          if (testChar == "t") then
           t1 = true
           end
          if (testChar == "j") then
           j1 = true
           end
         end
        end
        if (t1 == false) then
         local title = mw.title.getCurrentTitle()
         t1 = t1st[title.text] == true
        end

-- based on setting/preference specify order local orderlist = {"c", "s", "t", "p", "tp", "w", "j", "cy", "poj", "zhu", "l"} if (t1) then orderlist[2] = "t" orderlist[3] = "s" end if (j1) then orderlist[4] = "j" orderlist[5] = "cy" orderlist[6] = "p" orderlist[7] = "tp" orderlist[8] = "w" end -- rename rules. Rules to change parameters and labels based on other parameters if args["hp"] then -- hp an alias for p ([hanyu] pinyin) args["p"] = args["hp"] end if args["tp"] then -- if also Tongyu pinyin use full name for Hanyu pinyin labels["p"] = "Hanyu Pinyin" end if (args["s"] and args["s"] == args["t"]) then -- Treat simplified + traditional as Chinese if they're the same args["c"] = args["s"] args["s"] = nil args["t"] = nil elseif (not (args["s"] and args["t"])) then -- use short label if only one of simplified and traditional labels["s"] = labels["c"] labels["t"] = labels["c"] end local body = "" -- the output string local params -- for creating HTML spans local label -- the label, i.e. the bit preceeding the supplied text local val -- the supplied text -- go through all possible fields in loop, adding them to the output for i, part in ipairs(orderlist) do if (args[part]) then -- build label label = "" if (uselabels) then label = labels[part] if (capfirst) then label = mw.language.getContentLanguage():ucfirst( but gelatin has not been entirely replaced. The light-exposed crystals are reduced by the developer to black metallic silver particles that form the image. Colour films and papers usually have multiple layers of emulsion, with dye couplers added. Layers of dye are coated between emulsion layers to act as optical filters.

Manufacture

A solution of silver nitrate is mixed into a warm gelatin solution containing potassium bromide, sodium chloride or other alkali metal halides. A reaction precipitates fine crystals of insoluble silver halides that are light-sensitive. The silver halide is actually being 'peptized' by the gelatin. The type and quantity of gelatin used influences the final emulsion's properties. A pH buffer, crystal habit modifier, metal dopants, ripener, ripening restrainer, surfactants, defoamer, emulsion stabilizer and biocide are also used in emulsion making.

Most modern emulsions are "washed" to remove some of the reaction byproducts (potassium nitrate and excess salts). The "washing" or desalting step can be performed by ultrafiltration, dialysis, coagulation (using acylated gelatin), or a classic noodle washing method.

Emulsion making also incorporates steps to increase sensitivity by using chemical sensitizing agents and sensitizing dyes.

See also

References

  • Reilly, James M. Care and Identification of 19th-Century Photographic Prints. Eastman Kodak, Rochester, NY: 1986.

External links

  • Contemporary handcrafted silver gelatin emulsions
  • Contemporary photographic emulsion based on historical silver gelatin formula
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