american hand book of the daguerreotype-第20部分

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plate　have　not　been　thoroughly　washed　and　are　still　contaminated　with　the　soluble　chlorides　which　are　contained　in　the　solution。

〃From　the　fact　that　the　plate　if　prepared　with　positive　electricity　gives　a　positive　picture；　while　it　prepared　otherwise　it　gives　a　negative；　it　is　evident　that　electricity　plays　an　important　part　in　this　process。　The　same　is　true　to　some　extent　with　the　compounds　formed　with　iodine；　bromine。　　and　fluorine。

〃On　heating　the　plate；　the　brown　coating　of　chloride　melts　into　a　translucent　enamel；　and　the　heat　should　be　withdrawn　when　a　cherry…red　color　is　produced。　It　the　heat　is　continued　longer；　the　plate　assumes　a　lighter　color；　and　becomes　less　sensitive；　and　the　enamel　will　finally　scale　off。　To　produce　a　picture　by　the　ordinary　process　of　M。　Neipce；　unaccelerated；　it　should　be　exposed　for　from　three　to　five　hours　to　sunlight　in　the　camera；　though　pictures　may　be　procured　by　contact；　in　from　fifteen　to　thirty　minutes。〃


MULTIPLYING　DAGUERREOTYPES　ON　ONE　PLATE。

I　have　produced　some　interesting　specimens　of　the　Daguerreotypic　art；　by　exposing　in　the　camera　only　a　portion　of　the　sensitive　plate　to　the　action　of　light。　　When　on　the　exposed　portion　an　image　is　formed；　then　taking　the　tablet　into　the　dark　room；　change　ends　and　expose　the　sensitive　portion；　and　produce　another　image；　developing　as　usual。　This　plan　is　adapted　for　taking　likenesses　for　lockets。　Two　images　can　be　presented　as　sitting　side　by　side；　by　covering　half　the　plate　with　black　paper；　and　exposing　as　before。　In　this　manner　we　have　been　enabled　to　surprise　persons　by　exhibiting　their　portrait　on　the　same　plate　with　a　stranger's。　Daguerreotypists　must　be　cautious　in　practicing　this；　as　it　might　not　be　agreeable　to　the　parties　whose　likenesses　are　together；　by　the　above　process。　It　is　impossible　to　produce　an　impression　without　a　line　being　seen　where　the　edge　of　the　paper　prevented　the　operation　of　the　light。

I　have　recently　seen　a　fine　specimen　produced　by　another　plan；　which　far　exceeds　the　above；　there　being　no　line；　or　any　peculiarity　denoting　two　exposures。　　The　specimen　referred　to；　was　a　gentleman　represented　on　one　plate　by　two　full　length　portraits。　This　was　produced　by　using　a　black　velvet　for　the　background。　The　plate　was　exposed　sufficient　time　to　produce　one　impression；　and　then　the　gentleman　assumed　another　position；　and　is　repeated　as　looking　at　himself。　　From　the　fact　that　the　time　required　to　develop　black　velvet　being　so　much　longer　than　that　for　producing　a　portrait；　we　are　enabled　to　produce　the　above　interesting　results。


DEPOSIT　IN　GILDING。

Regarding　specks　from　bad　water；　I　would　remark　that　gilding　should　be　made　only　with　distilled　water。　　Thus　made；　it　produces　very　little　deposit；　even　by　long　keeping。　It　therefore　preserves　its　original　strength；　and　works　with　great　uniformity。

Every　grain　of　deposit　contains　at　least　7…10　its　weight　of　gold；　easily　discoverable　by　the　blowpipe。　Such　gilding　is　continually　deteriorating；　which　with　good　chloride　and　distilled　water　may　be　prevented。　Distilled　water　should　also　be　used　for　the　hyposulphite。　and　for　cleaning　plates。　　Any　good；　clear　water　may　be　afterwards　used　for　washing　off；　with　equally　good　results。　I　am　very　rarely　troubled　with　specs；　and　deem　this　as　the　main　reason。

With　a　portable　still　attached　to　a　cooking　stove；　I　obtain　half　a　gallon　of　water　per　hour；　and　with　very　little　trouble。　A　small　tin　retort　or　still　connected　with　a　Leibig's　condenser；　would　not　add　much　to　the　〃traps〃　of　the　travelling　operator；　and　save　him　many　a　disreputable　specimen。T。　J。　BAILEY。　Humphrey's　Journal。


PRACTICAL　HINTS　ON　THE　DAGUERREOTYPE。

The　following　is　from　Humphrey's　Journal；　vol。　　5；　and　from　the　pen　of　Dr。　WM。　HARRINGTON；　one　of　the　most　able　writers　upon　the　subject　of　the　Daguerreotype　in　this　country：


THE　CAUSE　OF　THE　DIFFICULTY　THAT　SOMETIMES　OCCURS　TO　PREVENT　THE　PRODUCTION　OF　A　CLEAR　IMPRESSION　UPON　A　DAGUERREOTYPE　PLATE。

Beyond　all　doubt　this　is　traceable　to　dampness。　Truly　this　is　not　a　new　thought；　but　where　does　this　dampness　come　from？　　How　does　it　originate；　and　where　is　it　located？　Generally　it　has　been　referred　to　a　point　entirely　remote　from　its　real　location。

This　dampness　exists　particularly　upon　the　surface　of　the　plate；　is　obviously　derived　immediately　from　the　atmosphere；　and　is　owing　to　a　certain　relative　temperature　of　the　plate　with　the　hygrometric　condition　of　the　atmosphere。

Whenever　this　relation　exists　between　the　plate　and　atmosphere；　a　precipitation　of　moisture　takes　place　upon　the　surface　of　the　plate；　which　render　all　efforts　at　polishing　impracticable。　This　interference　is　not　confined　to　the　buffing　operation　alone；　but　sometimes　is　discoverable　even　in　the　ordinary　process　of　scouring。　Every　one　at　all　experienced　in　this　art　will　remember　that　it　is　not　always　an　easy　matter　for　him；　by　scouring；　to　bring　his　plate　to　the　desired　lustre。　　All　his　efforts　become　unavailing；　the　more　he　rubs；　the　duller　the　surface　of　his　plate　appears；　and　although　he　renews　his　cotton　repeatedly；　still　he　is　obliged　to　content　himself　with　an　unsatisfactory　finish。

This　relative　condition　is　not　confined　to　any　particular　season　of　the　year；　nor　to　any　certain　thermometric　temperature；　but　may　occur　in　summer　as　well　as　in　winter；　the　weather　being　warm　or　cold；　wet　or　dry；　clear　or　cloudy；　raining　or　shining。　Under　any　of　these　circumstances；　if　the　relation　of　the　plate　and　atmosphere　be　such　as　to　invite　upon　the　plate　a　precipitation　of　humidity　from　the　atmosphere；　the　prospect　of　producing　a　clear　impression　is　quite　problematical。

It　is　reasonable　to　expect　this　occurrence　from　the　fact　that　metal　is　a　good　radiator；　and　radiation　reduces　the　temperature　of　a　metallic　body　below　that　of　the　atmosphere。　　Consequently；　if　this　relative　condition　happens；　the　result　will　be　as　I　have　stated。

Bodies　may　be　colder　than　the　atmosphere　and　yet　derive　no　moisture　from　it；　while　at　the　same　time　the　driest　atmosphere　is　not　devoid　of　moisture；　but　will　part　with　it　under　certain　conditions。

Assuming　for　granted　that　this　relative　condition　between　the　plate　and　atmosphere；　disposing　the　former　to　receive　the　humidity　of　the　latter；　constitutes　the　great　obstacle　the　operator　has　to　contend　with　in　producing；　a　clear　proof　upon　the　plate；　the　remedy　naturally　suggests　itself；　and　is　very　simple。　　It　consists　in　merely　heating　the　plate　above　the　temperature　of　the　atmosphere；　previous　to　polishing；　and　retaining　that　temperature　during　the　operation。　Various　measures　might　be　devised　to　effect　the　desired　object；　one　of　which　consists　of　a　sheet…iron　box；　heated　from　the　inside　by　a　spirit…lamp；　upon　the　top　of　which　are　to　be　kept　the　plates　ready　to　undergo　the　process　of　being　polished；　the　blocks　of　the　swing　or　any　other　vice；　or　the　iron　bed　belonging　to　Lewis's　vice。

In　cold　weather；　when　it　is　necessary　to　keep　a　fire　in　the　preparation　room；　all　of　the　above　may　be　so　arranged　in　the　vicinity　of　the　fire　as　to　receive　the　requisite　degree　of　heat　for　the　purpose　specified。

This　part　of　the　subject；　however；　is　left　entirely　for　the　ingenuity　of　the　operator。　　No　matter　by　hat　means　he　accomplishes　the　object；　all　that　is　required　is　to　heat　the　plate　above　the　temperature　of　the　atmosphere　and　retain　that　heat　during　the　process　of　polishing。

Since　the　adoption　of　this　method。　　in　connection　with　my　partner；　T。　J。　Dobyns；　even　in　this　humid　climate　of　ours；　when　everything　in　the　room　is　dripping　with　moisture；　it　has　been　attended　with　invariable　success。


CHOICE　OF　PLATES；　ETC。

In　the　great　catalogue　of　complaints　made　by　operators；　none　is　more　common　than　that　alleged　against　the　quality　of　plates　in　general　use。　　Although　the　greatest　diversity　of　opinion　exists　upon　this　subject；　nevertheless　the　plates　of　every　manufactory　share　in　this　universal　condemnation。

To　be　sure　it　cannot　be　denied　but　that　this　necessary　article　of　utility　in　the　photographic　art　has　undergone　a　sad　deterioration　in　quality　owing　to　the　increasing　demand　and　great　reduction　in　price　the　plates　of　the　present　day　being　by　no　means　so　heavily　coated　with　silver　as　formerlybut　the　complaint　alluded　to　is　not　predicated　so　much　upon　the　thinness　of　silver　as　upon　a　mysterious　something　which　has　conferred　upon　the　plates　the　epithet　of　not　good。

That　this　complaint　is　in　a　great　measure　groundless　appears　evident　from　the　fact　that　while；　with　the　same　brand　of　plates　one　operator　can　work　successfully；　another　encounters　the　greatest　difficulty；　while　one　is　able　to　produce　beautifully　clear　and　altogether　satisfactory　results；　the　other　labors　under　the　troublesome　annoyance　of　innumerable　specks；　large　dark　insensitive　patches　and　brown　map…like　portions；　together　with　divers　other　blemishes；　sufficient　to　prevent　him　from　obtaining　anything　like　a　tolerable　impression。

From　this　wide　difference　in　the　results　of　the　two　operators　using　identically　the　same　article；　it　is　but　reasonable　to　conclude　that　the　complaint　is　founded　in　error；　while　the　inference　is　no　more　than　just；　that　the　fault　may　be　traced　to　a　want　of　practical　skill　on　the　part　of　the　complaining　operator　himself；　rather　than　to　the　inferior　quality　of　the　plates。

The　question；　then；　whether　the　plates　are　unfit　for　use；　or　whether　those　who　pronounce　them　so　understand　how　to　use　them；　appears　to　be　satisfactorily　answered。　It　therefore　becomes　a　matter　worthy　of　investigation；　to　ascertain　what　superior　judgment　and　skill　one　operator　possesses　over　another　which　enable　him　to　work　successfully　a　quality　of　plate；　pronounced　by　the　other　entirely　useless。

Suppose　we　make　a　critical　examination　of　one　of　the　repudiated　plates。　From　its　external　appearance　we　have　little　hesitation　in　pronouncing　it　to　be　French；　indeed；　this　presumption　is　strongly　corroborated　by　the　fact　that　it　is　ornamented　upon　one　of　its　corners　with　a　brand　to　designate　the　manufactory　from　which　it　emanated。

Upon　close　inspection　we　cannot　fail　to　notice　a　striking　peculiarity　upon　the　surface；　the　roughness　is　very　remarkable；　the　planishing　hammer　has　left　amazingly　visible　indications　of　its　busy　work。　One　would　suppose　the　manu