the history and practice of the art of photography-第15部分

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Instead　of　wax；　boiled　linseed　oilit　must　be　the　best　and　most　transparent　kindmay　be　used。　　The　back　of　the　negative　photograph　should　be　smeared　with　the　oil；　and　then　placed　between　sheets　of　bibulous　paper。　When　dry　the　paper　is　highly　transparent。

IV。　APPLICATION　OF　PHOTOGENIC　DRAWING。This　method　of　photogenic　drawing　may　be　applied　to　useful　purposes；　such　as　the　copying　of　paintings　on　glass　by　the　light　thrown　through　them　on　the　prepared　paper　Imitations　of　etchings；　which　may　be　accomplished　by　covering　a　piece　of　glass　with　a　thick　coat　of　white　oil　paint；　when　dry；　with　the　point　of　a　needle；　lines　or　scratches　are　to　be　made　through　the　white　lead　ground；　so　as　to　lay　the　glass　bare；　then　place　the　glass　upon　a　piece　of　prepared　paper；　and　expose　it　to　the　light。　　Of　course　every　line　will　be　represented　beneath　of　a　black　color；　and　thus　an　imitation　etching　will　be　produced。　It　is　also　applicable　to　the　delineation　of　microscopic　objects；　architecture；　seulpture；　landscapes　and　external　nature。

A　novel　application　of　this　art　has　been　recently　suggested；　which　would　doubtless　prove　useful　in　very　many　instances。　By　rendering　the　wood　used　for　engravings　sensitive　to　light；　impressions　may　be　at　once　made　thereon；　without　the　aid　of　the　artist's　pencil。　　The　preparation　of　the　wood　is　simply　as　follows：Place　its　face　or　smooth　side　downwards；　in　a　plate　containing　twenty　grains　of　common　salt　dissolved　in　an　ounce　of　water；　here　let　it　remain　for　five　minutes；　take　it　out　and　dry　it；　then　place　it　again　face　downwards　in　another　plate　containing　sixty　grains　of　nitrate　of　silver　to　an　ounce　of　water；　here　let　it　rest　one　minute；　when　taken　out　and　dried　in　the　dark　it　will　be　fit　for　use；　and　will　become；　on　exposure　to　the　light；　of　a　fine　brown　color。　Should　it　be　required　more　sensitive；　it　must　be　immersed　in　each　solution　a　second　time；　for　a　few　seconds　only。　It　will　now　be　very　soon　effected　by　a　very　diffused　light。

This　process　may　be　useful　to　carvers　and　wood　engravers　not　only　to　those　who　cut　the　fine　objects　of　artistical　design；　but　still　more　to　those　who　cut　patterns　and　blocks　for　lace；　muslin；　calico…printing；　paper　hangings；　etc。；　as　by　this　means　the　errors；　expense　and　time　of　the　draughtsman　may　be　wholly　saved；　and　in　a　minute　or　two　the　most　elaborate　picture　or　design；　or　the　most　complicated　machinery；　be　delineated　with　the　utmost　truth　and　clearness。



CHAP。　IX。

CALOTYPE　AND　CHRYSOTYPE。


The　materials　and　apparatus　necessary　for　the　Calotype　process　are

Two　or　Three　Shallow　Dishes；　for　holding　distilled　water；　iodide；　potassium；　&c。the　same　water　never　being　used　for　two　different　operations。

White　Bibulous　Paper。

Photogenic　CameraFig。　9。

Pressure　FrameFig　29。

Paper；　of　the　very　best　qualitydirections　for　the　choice　of　which　have　been　already　given。

A　Screen　of　Yellow　Glass。

Camels'　or　Badgers'　hair　Brushes：A　seperate　one　being　kept　for　each　wash　and　solution；　and　which　should　be　thoroughly　cleansed　immediately　after　using　in　distilled　water。　That　used　for　the　gallo…nitrate　is　soon　destroyed；　owing　to　the　rapid　decomposition　of　that　preparation。

A　Graduated　Measure。

Three　or　Four　Flat　Boards；　to　which　the　paper　may　be　fixed　with　drawing　pins。

A　Hot　Water　Drying　Apparatus；　for　drying　the　paper　will　also　be　found　useful。

In　preparing　the　Calotype　paper；　it　is　necessary　to　be　extremely　careful；　not　only　to　prevent　the　daylight　from　impringing　upon　it；　but　also　to　exclude；　if　possible；　the　strong　glare　of　the　candle　or　lamp。　This　may　be　effected　by　using　a　shade　of　yellow　glass　or　gauze；　which　must　be　placed　around　the　light。　　Light　passing　through　such　a　medium　will　scarcely　affect　the　sensitive　compounds；　the　yellow　glass　intercepting　the　chemical　rays。

Preparation　of　the　Iodized　Paper。Dissolve　one　hundred　grains　of　crystalized　nitrate　of　silver　in　six　ounces　of　distilled　water；　and　having　fixed　the　paper　to　one　of　the　boards；　brush　it　over　with　a　soft　brush　on　one　side　only　with　this　solution；　a　mark　being　placed　on　that　side　whereby　it　may　be　known。　When　nearly　dry　dip　it　into　a　solution　of　iodide　of　potassium；　containing　five　hundred　grains　of　that　salt　dissolved　in　a　pint　of　water。　When　perfectly　saturated　with　this　solution；　it　should　be　washed　in　distilled　water；　drained　and　allowed　to　dry。　　This　is　the　first　part　of　the　process；　and　the　paper　so　prepared　is　called　iodized　paper。　It　should　be　kept　in　a　port…folio　or　drawer　until　required：　with　this　care　it　may　be　preserved　for　any　length　of　time　without　spoiling　or　undergoing　any　change。

Mr。　Cundell　finds　a　stronger　solution　of　nitrate　of　silver　preferable；　and　employs　thirty　grains　to　the　ounce　of　distilled　water：　he　also　adds　fifty　grains　of　common　salt　to　the　iodide　of　potassium；　which　he　applies　to　the　marked　side　of　the　paper　only。　This　is　the　first　process。

Preparation　of　the　paper　for　the　Camera。The　second　process　consists　in　applying　to　the　above　a　solution　which　has　been　named　by　Mr。　Talbot　the　〃Gallo…Nitrate　of　Silver；〃　it　is　prepared　in　the　following　manner：　Dissolve　one　hundred　grains　of　crystalized　nitrate　of　silver　in　two　ounces　of　distilled　water；　to　which　is　added　two　and　two…third　drachms　of　strong　acetic　acid。　　This　solution　should　be　kept　in　a　bottle　carefully　excluded　from　the　light。　　Now；　make　a　solution　of　gallic　acid　in　cold　distilled　water：　　the　quantity　dissolved　is　very　small。　When　it　is　required　to　take　a　picture；　the　two　liquids　above　described　should　be　mixed　together　in　equal　quantities；　but　as　it　speedily　undergoe　decomposition；　and　will　not　keep　good　for　many　minutes；　only　just　sufficient　for　the　time　should　be　prepared；　and　that　used　without　delay。　It　is　also　well　not　to　make　much　of　the　gallic　acid　solution；　as　it　will　not　keep　for　more　than　a　few　days　without　spoiling。　A　sheet　of　the　iodized　paper　should　be　washed　over　with　a　brush　with　this　mixed　solution；　care　being　taken　that　it　be　applied　to　the　marked　side。　This　operation　must　be　performed　by　candle　light。　　Let　the　paper　rest　half　a　minute；　then　dip　it　into　one　of　the　dishes　of　water；　passing　it　beneath　the　surface　several　times；　it　is　now　allowed　to　drain；　and　dried　by　placing　its　marked　side　upwards；　on　the　drying　apparatus。　It　is　better　not　to　touch　the　surface　with　bibulous　paper。　It　is　now　highly　sensitive；　and　ready　to　receive　the　impression。　In　practice　it　is　found　better　and　more　economical　not　to　mix　the　nitrate　of　silver　and　gallic　acid；　but　only　to　brush　the　paper　with　the　solution　of　the　nitrate。

Mr。　Talbot　has　recently　proposed　some　modifications　in　his　method　of　preparing　the　calotype　paper。　　The　paper　is　first　iodized　in　the　usual　way；　it　is　then　washed　over　with　a　saturated　solution　of　gallic　acid　in　distilled　water　and　dried。　　Thus　prepared　he　calls　it　the　io…gallic　paper：　it　will　remain　good　for　a　considerable　time　if　kept　in　a　press　or　portfolio。　When　required　for　use；　it　is　washed　with　a　solution　of　nitrate　of　silver　（fifty　grains　to　the　ounce　of　distilled　water）；　and　it　is　then　fit　for　the　camera。

Exposure　in　the　Camera。The　calotype　paper　thus　prepared　possesses　a　very　high　degree　of　sensibility　when　exposed　to　light；　and　we　are　thus　provided　with　a　medium　by　which；　with　the　aid　of　the　photogenic　camera；　we　may　effectually　copy　views　from　nature；　figures；　buildings；　and　even　take　portraits　from　the　shadows　thrown　on　the　paper　by　the　living　face。　The　paper　may　be　used　somewhat　damp。　　The　best　plan　for　fixing　it　in　the　camera　is　to　place　it　between　a　piece　of　plate　glass　and　some　other　material　with　a　flat　surface；　as　a　piece　of　smooth　slate　or　an　iron　plate；　which　latter；　if　made　warm；　renders　the　paper　more　sensitive；　and　consequently　the　picture　is　obtained　more　rapidly。

Time　of　Exposure。With　regard　to　the　time　which　should　be　allowed　for　the　paper　to　remain　in　the　camera；　no　direct　rules　can　be　laid　down；　this　will　depend　altogether　upon　the　nature　of　the　object　to　be　copied；　and　the　light　which　prevails。　All　that　can　be　said　is；　that　the　time　necessary　for　forming　a　good　picture　varies　from　thirty　seconds　to　five　minutes；　and　it　will　be　naturally　the　first　object　of　the　operator　to　gain　by　experience　this　important　knowledge。

Bringing　Out　the　Picture。The　paper　when　taken　from　the　camera；　which　should　be　done　so　as　to　exclude　every　ray　of　lightand　here　the　dark　slide　of　the　camera　plate　holder　becomes　of　great　use　bears　no　resemblance　to　the　picture　which　in　reality　is　formed。　The　impression　is　latent　and　invisible；　and　its　existence　would　not　be　suspected　by　any　one　not　acquainted　with　the　process　by　previous　experiment。　　The　method　of　bringing　out　the　image　is　very　simple。　It　consists　in　washing　the　paper　with　the　gallo…nitrate　of　silver；　prepared　in　the　way　already　described；　and　then　warming　it　gently；　being　careful　at　the　same　time　not　to　let　any　portion　become　perfectly　dry。　　In　a　few　seconds　the　part　of　the　paper　upon　which　the　light　has　acted　will　begin　to　darken；　and　finally　grow　entirely　black；　while　the　other　parts　retain　their　original　color。　Even　a　weak　impression　may　be　brought　out　by　again　washing　the　paper　in　the　gallo…nitrate；　and　once　more　gently　warming　it。　When　the　paper　is　quite　black；　as　is　generally　the　case；　it　is　a　highly　curious　and　beautiful　phenomenon　to　witness　the　commencement　of　the　picture；　first　tracing　out　the　stronger　outlines；　and　then　gradually　filling　up　all　the　numerous　and　complicated　details。　The　artist　should　watch　the　picture　as　it　developes　itself；　and　when　in　his　judgment　it　has　attained　the　greatest　degree　of　strength　and　clearness；　he　shall　stop　further　proceedings　by　washing　it　with　the　fixing　liquid。　Here　again　the　mixed　solution　need　not　be　used；　but　the　picture　simply　brushed　over　with　the　gallic　acid。

The　Fixing　Process。In　order　to　fix　the　picture　thus　obtained；　first　dip　it　into　water；　then　partly　dry　it　with　bibulous　paper；　and　wash　it　with　a　solution　of　bromide　of　potassiumcontaining　one　hundred　grains　of　that　salt　dissolved　in　eight　or　ten　ounces　of　distilled　water。　The　picture　is　again　washed　with　distilled　water；　and　then　finally　dried。　Instead　of　bromide　of　potassium；　a　solution　of　hyposulphite　of　soda；　as　before　directed；　may　be　used　with　equal　advantage。

The　original　calotype　picture；　like　the