american hand book of the daguerreotype-第2部分

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one　is　liable　to　get　on　the　buff　and　scratch　the　plate。

Rest　the　fingers　of　the　left　hand　on　the　back　of　the　buff；　near　the　farther　end；　with　about　the　same　pressure　as　in　cleaning；　while　with　the　right　you　bear　on　the　handle　to　correspond；　and　give　the　buff　a　free；　easy；　horizontal　motion；　passing　it　very　nearly　the　whole　length　over　the　plate　each　time。　Continue　this　operation　in　such　a　manner　that　the　plate　will　on　all　parts　of　its　surface　have　received　an　equal　amount　of　polish。　This　buff　once　well　filled　with　polish；　add　but　little　after；　say　a　small　quantity　once　in　two　or　three　plates。　The　polish　as　well　as　the　buffs　must　be　kept　perfectly　dry。

The　second　buff　should　always　be　in　the　best　order；　and　if　this　is　the　case；　but　little　polish　after　the　first　need　be　used。　Much　depends　upon　the　last　finish　of　the　surface　of　the　plate；　and　as　a　fine　impression　is　desired　in　the　same　ratio；　the　operator　must　exercise　care　and　skill　in　this　operation。　Some　buff　the　smaller　plates　on　the　hands；　by　resting　them　on　the　fingers　in　such　a　manner　that　the　buff　cannot　touch　them；　some　by　holding　the　edges　with　thumb　and　little　finger；　with　the　remaining　fingers　under；　or　on　the　back；　and　others　buff　on　the　holder。　　When　this　last　method　is　adopted；　it　requires　the　greatest　caution　to　prevent　the　dust　from　getting　on　the　buff。　The　holder　should　be　wiped　clean。

The　plate　frequently　slips　off　or　around；　and　the　buff　comes　in　contact　with　the　bed　of　the　holder。　　When；　however；　the　operator　is　so　unfortunate　as　to　meet　with　this　mishap；　the　utmost　care　must　be　observed　in　thoroughly　cleaning　the　buff　cover　before　further　buffing。　　In　this　last　buffing　it　may　be　continued　as　before；　except　without　the　application　of　polish　powder　to　the　last　buff。　Examine　the　surface　occasionally；　and　buff　more　lightly　towards　the　close　of　the　operation；　using　at　last　the　mere　weight　of　the　buff。　This　last　buffing　should　occupy　as　long　a　time　as　the　first。

The　point　to　be　aimed　at　is；　the　production　of　a　surface　of　such　exquisite　polish　as　to　be　itself　invisible；　like　the　surface　of　a　mirror。　The　secret　of　producing　pictures　discernible　in　any　light；　lies　in　this：　the　more　dark；　deep　and　mirror…like　the　surface　of　the　plate；　the　more　nearly　do　we　approach　to　perfection。

In　all　cases；　very　light　and　long　continued　buffing　is　productive　of　the　greater　success；　since　by　that　means　a　more　perfect　polish　can　be　obtained。

The　question　is　often　asked；　why　is　it　that　the　plates　receive　the　coating　so　unevenly？　　I　will　answer　by　saying　that　it　may　arise　from　two　causes：　the　first　and　most　general　cause　is　that　those　parts　of　the　plate's　surface　which　will　receive　the　heaviest　coating　have　been　more　thoroughly　polished；　and　the　consequence　is　that　it　is　more　sensitive　to　the　chemical　operation。　　second。　　and　might　perhaps　be　considered　a　part　of　the　first；　the　heat　of　the　plate　may　not　be　equal　in　all　its　parts；　this　may　arise　from　the　heat　caused　by　the　friction　in　buffing。　It　is　a　well　known　fact；　with　which　every　observing　practitioner　is　familiar；　that　a　silver　plate　at　a　temperature　of　45　deg。　or　less；　exposed　to　the　vapors　of　iodine；　is　less　sensitive　and　takes　a　longer　time　to　coat；　than　when　it　is　at　a　temperature　of　60　deg。　or　more。

Whenever　a　view　is　to　be　taken；　or　any　impression　which　requires　the　plate　to　be　turned　on　the　side；　it　should　be　buffed　in　the　other　direction；　so　that　the　marks　will　always　be　horizontal；　when　the　picture　is　in　position。　With　the　finest　possible　polish；　the　plate　is　ready　for　the　coating　box。

The　question　is　often　asked　by　operators；　what　is　the　state　of　the　plate　when　polished　and　allowed　to　stand　for　a　time　before　using？　To　meet　this　point　we　hare　only　to　consider　the　silver　and　the　power　acting　upon　it。　　Pure　atmosphere　does　not　act　upon　silver；　but　we　do　not　have　this　about　in　our　operating　rooms；　as　it　is　more　or　less　charged　with　sulphurated　hydrogen；　which　soon　tarnishes　the　surface　of　the　plate　with　a　film　of　brown　sulphurate。　It　is　this　that　sometimes　causes　the　specks　which　appear　on　finishing　the　impression；　and　are　a　great　annoyance。　Hence　we　see　that　the　plate　should　be　buffed　just　before　receiving　the　vapor　of　iodine。　　Mr　Hunt　gives　his　opinion　of　the　use　of　diluted　nitric　acid　as　the　best　solution　for　freeing；　the　surface　of　the　plate；　he　says：

〃Numerous　experiments　on　plated　copper；　pure　silver　plates；　and　on　silvered　glass　and　paper；　have　convinced　me　that　the　first　operation　of　polishing　with　nitric　acid；　etc。；　is　essential　to　the　production　of　the　most　sensitive　surface。　All　who　will　take　the　trouble　to　examine　the　subject；　will　soon　be　convinced　that　the　acid　softens　the　silver；　bringing　it　to　a　state　in　which　it　is　extremely　susceptible　of　being　either　oxydized　or　iodized；　according　as　the　circumstances　may　occur　of　its　exposure　to　the　atmosphere　or　the　iodine。〃

I　cannot　see　the　objection　to　this　solution；　not；　however；　in　general　use。　Our　operators　do　not　find　it　of　sufficient　importance　to　the　success　of　their　pictures　to　accept　it；　the　alcoholic　solution　being　in　its　nature　less　objectionable。

I　will　say　here；　that　a　plate　submitted　to　only　an　ordinary　polish　is　found　to　contain　numberless　minute　particles　of　the　powder　made　use　of。　　Should　the　same　plate　be　buffed　for　a　long　time；　the　polish　will　nearly　all　disappear；　leaving　the　cavities　in　the　surface　free　for　the　action　of　agents　employed　in　subsequent　operation。　　For　this　reason；　I　find　that　great　amount　of　polishing　powder　should　not　be　applied　to　the　last　buff；　and　it　is　obvious　that　three　buffs　can　be　employed　to　adventure；　the　two　last　should　not　receive　any　polishing　materials。　I　have　examined　a　plate　that　was　considered　to　possess　a　fine　finish；　and　similar　had　produced　good　impressions；　these　same　plates；　when　subjected　to　a　long　and　light　buffing；　would　present　a　surface　no　finer　in　appearance　to　the　naked　eye；　but　upon　exposure　to　the　solar　radiation；　would　produce　a　well…defined　image　in　one　fourth　less　time　than　the　plate　without　the　extra　buffing。

Coating　the　Plate。For　this　purpose　our　mechanics　and　artists　have　provided　a　simple　apparatus　called　a　coating…box；　which　is　so　arranged　as　to　be　perfectly　tight；　retaining　the　vapor　of　the　iodine　or　accelerators；　and　at　the　same　time　allowing；　by　means　of　a　slide；　the　exposure　of　the　plate　to　these　vapors。　They　can　readily　be　obtained　by　application　to　any　dealer；　all　of　whom　can　furnish　them。

The　principal　difficulty　in　coating　the　plate；　is　that　of　preserving　the　exact　proportion　between　the　quantity　of　iodine　and　bromine；　or　quick。　It　is　here　necessary　to　say；　that　hardly　any　two　persons　see　alike　the　same　degree　of　color；　so　as　to　be　enabled　to　judge　correctly　the　exact　tint；　i。　　e。　　what　one　might　describe　as　light　rose　red；　might　appear　to　another　as　bright　or　cherry　red；　consequently；　the　only　rule　for　the　student　in　Daguerreotype；　is　to　study　what　appears　to　him　to　be　the　particular　tint　or　shade　required　to　aid　him　to　produce　the　desired　result。　Practise　has　proved　that　but　a　slight　variation　in　the　chemical　coating；　of　the　Daguerreotype　plate　will　very　materially　affect　the　final　result。

The　operator　will　proportion　the　coating　of　iodine　and　bromine　or　accelerators　according　to　the　strength　and　composition　of　the　latter。

Experience　proves　that　the　common　impressions；　iodized　to　a　rather　light　yellow　gold　tint；　and　brought　by　the　bromine　to　a　very　light；　rose　color；　have　their　whites　very　intense；　and　their　deep　shades　very　black。　It　is　also　known　that　if　you　employ　a　thicker　coating　of　iodine　and　apply　upon　it　a　proportionate　tint　of　bromine；　so　as　to　obtain　a　deep　rose　tint；　delineations　will　be　less　marked；　and　the　image　have　a　softer　tone。　This　effect　has　been　obvious　to　everyone　who　has　practised　the　art。　Thus　I　may　observe　that　the　light　coatings　produce　strong　contrast　of　light　and　shade；　and　that　this　contrast　grows　gradually　less；　until　in　the　very　heavy　coating　it　almost　wholly　disappears。　From　this　it　will　readily　be　perceived　that　the　middle　shades　are　the　ones　to　be　desired　for　representing　the　harmonious　blending　of　the　lights　and　shades。

Then；　if　we　examine；　with　respect　to　strength；　or　depth　of　tone；　and　sharpness　of　impression；　we　see　that　the　light　coating；　produces　a　very　sharp　but　shallow　impression；　while　the　other　extreme　gives　a　deep　but　very　dull　one。　Here；　then；　are　still　better　reasons　for　avoiding　either　extreme。　The　changes　through　which　the　plate　passes　in　coating　may　be　considered　a　yellow　straw　color　or　dark　orange　yellow；　a　rose　color　more　or　less　dark　in　tint；　or　red　violet；　steel　blue　or　indigo；　and　lastly　green。　After　attaining　this　latter　color；　the　plate　resumes　a　light　yellow　tint；　and　continues　to　pass　successively　a　second　time；　with　very　few　exceptions；　through　all　the　shades　above　mentioned。

I　will　here　present　some　excellent　remarks　upon　this　subject　by　Mr。　Finley。　This　gentleman　says：

〃It　is　well　known　to　all　who　have　given　much　attention　to　the　subject；　that　an　excess　of　iodine　gives　the　light　portions　of　objects　with　peculiar　strength　and　clearness；　while　the　darker　parts　are　retarded；　as　it　were；　and　not　brought　out　by　that　length　of　exposure　which　suffices　for　the　former。　　Hence；　statuary；　monuments；　and　all　objects　of　like　character；　were　remarkably　well　delineated　by　the　original　process　of　Daguerre；　the　plate　being　coated　with　iodine　alone。　An　excess　of　bromine；　to　a　certain　degree；　has　the　opposite　effect；　the　white　portions　of　the　impression　appearing　of　a　dull；　leaden　hue；　while　those　which　should　be　black；　or　dark；　appear　quite　light。　This　being　the　case；　I　conclude　there　must　be　a　point　between　the　two　extremes　where　light　and　dark　objects　will　be　in　photogenic　equilibrium。　The　great　object；　therefore；　is　to　maintain；　as　nearly　as　possible；　a　perfect　balance　between　the　two　elements　entering　into　union　to　form　the　sensitive　coating　of　the　plate；　in　order　that　the　lights　and　shades　be　truly　and　faithfully　represented；　and　that　all　objects；　whether　light　or　dark；　be　made　to　appear　so　far　conformable　to　nature；　as　is　consistent　with　the　difference　in　the　photogenic　energy　of　the　different　colored　rays　of　light。　　It　is　this　nicely…balanced　combination　which　ensures；　in　the　highest　degree；　a　union