american hand book of the daguerreotype-第17部分

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n　water；　in　which　a　little　soda　is　dissolved；　and　as　soon　as　the　surface　is　of　a　fine　silvery　whiteness；　it　is　to　be　dried　with　a　very　clean　warm　cloth。　　In　this　state　the　plates　may　be　kept　for　use。　　The　first　process　is　to　expose　the　plate　to　the　heat　of　a　spirit　flame；　until　the　silvered　surface　becomes　of　a　well…defined　golden…yellow　color；　then；　when　the　plate　is　cold；　take　a　piece　of　cotton；　dipped　in　very　dilute　nitric　acid；　and　rub　lightly　over　it　until　the　white　hue　is　restored；　and　dry　it　with　very　soft　clean　cloths。　　A　weak　solution　of　the　hydriodate　of　potash；　in　which　a　small　portion　of　iodine　is　dissolved；　is　now　passed　over　the　plate　with　a　wide　camel's　hair　brush。　　The　silver　is　thus　converted；　over　its　surface；　into　an　ioduret　of　silver；　and　in　this　state　it　is　exposed　to　light；　which　blackens　it。　When　dry；　it　is　to　be　again　polished；　either　with　dilute　acid　or　a　solution　of　carbonate　of　soda；　and　afterwards　with　dry　cotton；　and　the　smallest　possible　portion　of　prepared　chalk：　by　this　means　a　surface　of　the　highest　polish　is　produced。　The　rationale　of　this　process　is；　in　the　first　place；　the　heat　applied　dries　off　any　adhering　acid；　and　effects　more　perfect　union　between　the　copper　and　silver；　so　as　to　enable　it　to　bear　the　subsequent　processes。　　The　first　yellow　surface　appears　to　be　an　oxide　of　silver　with；　possibly；　a　minute　quantity　of　copper　in　combination；　which　being　removed　leaves　a　surface　chemically　pure。

Another　Method。The　best　and　simplest　mode　with　which　we　are　acquainted　is　to　divide　an　earthenware　vessel　with　a　diaphragm：　one　side　should　be　filled　with　a　very　dilute　solution　of　sulphuric　acid；　and　the　other　with　either　a　solution　of　ferroprussiate　of　potash；　or　muriate　of　soda；　saturated　with　chloride　of　silver。　　The　copper　plate；　varnished　on　one　side；　is　united；　by　means　of　a　copper　wire；　with　a　plate　of　zinc。　　The　zinc　plate　being　immersed　in　the　acid；　and　the　copper　in　the　salt；　a　weak　electric　current　is　generated；　which　precipitates　the　silver　in　a　very　uniform　manner　over　the　entire　surface。

Another　Method。A　piece　of　brass　or　of　polished　copper；　brass　is　preferred；　is　perfectly　planished　and　its　surface　made　perfectly　clean。　A　solution　of　nitrate　of　silver；　so　weak　that　the　silver　is　precipitated　slowly；　and　a　brownish　color；　on　the　brass；　is　laid　uniform＇v　over　it；　〃at　least　three　times；〃　with　a　camel's　hair　pencil。　After　each　application　of　the　nitrate；　the　plate　should　be　rubbed　gently　in　one　direction；　with　moistened　bitartrate　of　potassa；　applied　with　buff。　This　coat　of　silver　receives　a　fine　polish　from　peroxide　of　iron　and　buff。　Proofs　are　said　to　have　been　taken　on　it；　comparable　with　those　obtained　on　French　plates。


M。　SOLIEL'S　PROCESS　FOR　DETERMINING　THE　TIME　OF　EXPOSURE　IN　THE　CAMERA。

M。　Soliel　has　proposed　the　use　of　the　chloride　of　silver　to　determine　the　time　required　to　produce　a　good　impression　on　the　iodated　plate　in　the　camera。　His　method　is　to　fix　at　the　bottom　of　a　tube；　blackened　within；　a　piece　of　card；　on　which　chloride　of　silver；　mixed　with　gum　or　dextrine；　is　spread。　The　tube　thus　disposed　is　turned　from　the　side　of　the　object　of　which　we　wish　to　take　the　image；　and　the　time　that　the　chloride　of　silver　takes　to　become　of　a　greyish　slate　color　will　be　the　time　required　for　the　light　of　the　camera　to　produce　a　good　effect　on　the　iodated　silver。


INSTANTANEOUS　PROCESS　FOR　PROCURING　DAGUERREOTYPES。

The　following　method　of　producing　Daguerreotypes　has　by　some　been　named　as　above。　　Most　experienced　operators　have　been　long　acquainted　with　the　effect　of　the　vapor　of　ammonia　upon　the　chemically　coated　plate。　I　will　here　insert　Mr。　W。　H。　Hewett's　plan　of　proceeding。　This　gentleman；　in　referring　to　it　（published　in　1845）；　says：

〃This　improvement　consists　in　using　the　vapor　of　ammonia；　as　an　object　to　accelerate　the　action　of　light　upon　the　plate。　The　effect　is　produced　upon　a　simple　iodized　plate；　but　still　more　upon　a　plate　prepared　in　the　ordinary　way；　with　both　iodine　and　bromine。　By　this　means；　the　author　obtained　impressions　instantaneously　in　the　sunshine；　and　in　five　to　ten　seconds　in　a　moderate　light；　and　he　hopes　to　be　able　to　take　moving　objects。　　It　can　be　applied　by　exposing　the　prepared　plate　over　a　surface　of　water；　to　which　a　few　drops　of　ammonia　have　been　added　（sufficient　to　make　it　smell　of　ammonia）；　or　the　vapor　can　be　introduced　into　the　camera　during　the　action。　In　fact；　the　presence　of　ammonia；　in　the　operating…room；　appears　to　have　a　good　effect；　as　it　also　neutralizes　the　vapors　of　iodine　and　bromine　that　may　be　floating　about；　and　which　are　so　detrimental　to　the　influences　of　light　upon　the　plate。〃


GALVANIZING　THE　DAGUERREOTYPE　PLATE。

In　consideration　of　the　importance　of　galvanized　plates；　I　shall　endeavor　to　give　as　plain　and　concise　a　manner　of　manipulation　as　possible。　For　some　time　it　was　a　question　among　the　operators　generally；　as　to　the　beneficial　result　of　electrotyping；　the　Daguerreotype　plate；　but　for　a　few　years　past　our　first　operators　have　found　it　a　fact；　that　a　well　electro…silvered　surface　is　the　best　for　producing　a　portrait　by　the　Daguerreotype。

From　my　own　experiments；　I　have　found　that　a　plate；　by　being　galvanized；　can　be　rendered　more　sensitive　to　the　operation　of　the　light　in　proportion　of　one　to　five；　viz。：　if　a　plate　as　furnished　by　the　market；　be　cleaned；　polished；　coated　and　exposed　in　the　camera；　if　the　required　time　to　freely　develop　an　impression　be　ten　seconds；　a　similar　plate　prepared　in　like　manner　and　galvanized；　will　produce　an　equally　well…defined　image　in　eight　seconds。　In　connection　with　this　subject；　there　is　one　fact　worthy　of　notice；　a　plate　with　a　very　heavy　coating　of　pure　silver；　will　not　produce　an　equally　developed　image；　as　a　plate　with　a　thinner　coating；　hence　the　thin　coating；　providing　it　entirely　covers　the　surface；　is　the　best；　and　is　the　one　most　to　be　desired。　　The　experiment　is　plain　and　simple。　Let　the　slate　receive　a　heavy　or　thick　coating　by　the　electrotype；　then　polish；　coat；　expose　in　the　usual　manner；　and　the　result　will　be　a　flat；　ashy；　indistinct　impression；　when；　on　the　other　hand；　the　thin　coating　will　produce　a　bright；　clear　and　distinct　image；　with　all　the　details　delineated。

The　style　of　battery　best　for　the　purpose　has　been；　and　now　is；　a　question　of　dispute　among　operators；　some　preferring　the　Daniell　battery　to　Smee's。　Some　claim　the　superiority　of　the　first　from　its　uniformity　of　action；　others；　of　the　latter；　for　its　strength。　I　consider　either　good；　and　for　the　inexperienced　would　prefer　the　Daniell。　This　is　more　simple　in　its　construction；　while　it　has　certainty　in　action。　The　more　skillful　electrotyper　would　prefer　Smee's；　and　this　is　the　one　most　generally　in　use。　　I　would　remark　that　the　plan　of　galvanizing　plates　should　be　followed　by　every　operator；　and　when　once　thoroughly　tested；　no　one　will　abandon　it。


SILVERING　SOLUTION。

To　any　desired　quantity　of　chloride　of　silver　in　water　add；　little　by　little；　cyanide　of　potassium；　shaking　well　at　each　addition；　until　all　the　cyanide　is　dissolved。　　Continue　this　operation；　and　add　the　cyanide；　until　all　the　precipitate　is　taken　up　and　held　in　solution。

This　solution　is　now　ready　for　the　plate…cup。　Enough　water　may　be　added　to　cover　any　sized　plate　when　held　perpendicular　in　the　cup。　The　strength　of　the　solution　may　be　kept　up　by　occasionally　adding　the　chloride　of　silver　and　cyanide　of　potassium。　There　should　alway　be　a　very　little　excess　of　the　cyanide。

The　plate　should　be　well　cleaned　and　buffed；　and　the　solution　well　stirred　before　it　is　immersed。　　Care　should　be　observed　to　keep　the　solution　clean；　and　allow　no　particle　of　dust　to　come　in　contact　with　the　surface　of　the　plate。　The　plate　is　now　to　be　attached　to　the　pole　of　the　battery。

After　remaining　a　short　time；　it　assumes　a　blue　color；　take　it　out；　rinse　freely　with　pure　water；　then　dry　with　a　spirit　lamp；　and　it　is　ready　for　buffing。　　Buff　and　coat　in　the　usual　manner。　Some　operators　are　in　the　practice　of　immersing　the　plate　in　the　solution　and　buffing　twice。　　This　additional　silvering　is　no　improvement　wherever　there　has　been　a　proper　first　coating。

Sometimes　the　operator　is　troubled　with　streaks　or　scum　on　the　plate。　This　may　arise　from　three　causes；　all　of　which　experience　must　teach　the　experimenter　to　avoid；　first；　too　great　an　excess　of　cyanide　in　the　solution；　second；　a　lack　of　silver；　third；　the　current　too　strong。　Another　annoyance　arises　from　the　solution　being　dirty　and　the　dirt　collecting　on　the　surface。　　When　this　is　the　case；　the　dirt　is　sure　to　come　in　contact　with　the　surface　of　the　plate　as　it　is　plunged　into　the　solution；　and　the　result　is　a　scum　that　it　is　difficult　to　dispose　of。　This　can　be　prevented　only　by　frequent　filtering。　　One　thing　should　always　be　borne　in　mind　in　electrotyping　Daguerreotype　platesthat　in　order　to　secure　a　perfectly　coated　surface；　the　plate　should　be　perfectly　cleaned。　In　this　point；　many　who　have　tried　the　electrotype　process　have　failed；　attributing　their　ill　success　to　other　than　the　proper　cause。



DAGUERREOTYPES　WITHOUT　MERCURY。

The　following　process　possesses　some　interest；　and　is　worthy　a　trial　from　operators。　　M。　Natterer；　of　Vienna；　discovered　a　process　for　obtaining　proofs　on　iodized　plates　with　the　chloride　of　sulphur；　without　the　use　of　mercury。　A　plate　of　silver　is　iodized　in　the　usual　manner；　and　then　placed　on　the　top　of　a　vessel　six　or　eight　inches　high；　having　at　the　bottom；　in　a　small　cup；　a　few　drops　of　chloride　of　sulphur；　it　should　remain　exposed　to　the　action　of　the　vapor　until　the　sombre　yellow　color　is　changed　to　a　red；　after　which　it　is　brought　to　a　focus　m　the　camera；　where　it　is　exposed　to　the　light　in　the　camera；　for　about　the　time　necessary　to　produce　an　ordinary　daguerreotype。　　The　plate　is　then　taken　out　and　examined　in　the　camera　by　the　light　of　a　candle。　It　often　occurs　that　no　trace　of　the　image　is　as　yet　perceptible；　but　if　the　plate　is　heated　by　placing　over　a　spirit　lamp　the　unprepared　side；　or　if　left　for　some　time　in　the　dark；　or；　lastly；　if　exposed　only　a　few　seconds　to　a　weak；　dimmed　light；　the　positive　picture　then　appears　with　all　its　shades。　Of　these　three　modes　of　bringing　out　the　image；　the　second　is　superior　to　the　others。