the history and practice of the art of photography-第16节

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III。　PHOTOGENIC　PROCESS　ON　PAPER。Method。The　simplest　mode　is　to　procure　a　flat　board　and　a　square　of　glass；　larger　in　size　than　the　object　intended　to　be　copied。　On　the　board　place　the　photographic　paper　　＇hipho_29。gif＇　with　the　prepared　side　upwards；　and　upon　it　the　object　to　be　copied；　over　both　lay　the　glass　and　secure　them　so　that　they　are　in　close　connection　by　means　of　binding　screws　or　clamps；　similar　to　g。　g。　fig。　29。　　Should　the　object　to　be　copied　be　of　unequal　thickness；　such　as　a　leaf；　grass；　&c。；　it　will　be　necessary　to　place　on　the　board；　first；　a　soft　cushion；　which　may　be　made　of　a　piece　of　fine　flannel　and　cotton　wool。　By　this　means　the　object　is　brought　into　closer　contact　with　the　paper；　which　is　of　great　consequence；　and　adds　materially　to　the　clearness　of　the　copy。　The　paper　is　now　exposed　to　diffused　daylight；　or；　still　better；　to　the　direct　rays　of　the　sun；　when　that　part　of　the　paper　not　covered　by　the　object　will　become　tinged　with　a　violet　color；　and　if　the　paper　be　well　prepared；　it　will　in　a　short　time　pass　to　a　deep　brown　or　bronze　color。　　It　must　then　be　removed；　as　no　advantage　will　be　obtained　by　keeping　it　longer　exposed；　on　the　contrary；　the　delicate　parts　yet　uncolored　will　become　in　some　degree　affected。　　The　photogenic　paper　will　now　show　a　more　or　less　white　and　distinct　representation　of　the　object。　The　apparatus　figured　at　29　consists　of　a　wooden　frame　similar　to　a　picture　frame；　a　piece　of　plate　glass　is　fixed　in　front；　and　it　is　provided　with　a　sliding　cover　of　wood；　c。；　which　is　removed　when　the　paper　is　ready　to　be　exposed　to　the　action　of　the　light。　The　back；　d。；　which　is　furnished　with　a　cushion；　as　just　described；　is　made　to　remove　for　the　purpose　of　introducing　the　object　to　be　copied；　and　upon　it　the　prepared　paper；　the　back　is　then　replaced；　and；　by　aid　of　the　cross　piece　and　screw；　e。；　the　whole　is　brought　into　close　contact　with　the　glass。

The　objects　best　delineated　on　these　photographic　papers；　are　lace；　feathers；　dried　plants；　particularly　the　ferns；　sea…weeds　and　the　light　grasses；　impressions　of　copper　plate　and　wood　engravings；　particularly　if　they　have　considerable　contrast　of　light　and　shade（these　should　be　placed　with　the　face　downwards；　having　been　previously　prepared　as　hereafter　directed）　paintings　on　glass；　etchings；　&c。

To　fix　the　Drawings。Mr。　Talbot　recommends　that　the　drawings　should　be　dipped　in　salt　and　water；　and　in　many　instances　this　method　will　succeed；　but　at　times　it　is　equally　unsuccessful。　Iodide　of　potassium；　or；　as　it　is　frequently　called；　hydriodate　of　potash；　dissolved　in　water；　and　very　much　diluted；　（twenty…five　grains　to　one　ounce　of　water；）　is　a　more　useful　preparation　to　wash　the　drawings　with；　it　must　be　used　very　weak　or　it　will　not　dissolve　the　unchanged　muriate　only；　as　is　intended　but　the　black　oxide　also；　and　the　drawing　be　thereby　spoiled。

But　the　most　certain　material　to　be　used　is　the　hyposulphite　of　soda。　One　ounce　of　this　salt　should　be　dissolved　in　about　a　pint　of　distilled　water。　　Having　previously　washed　the　drawing　in　a　little　lukewarm　water；　which　of　itself　removes　a　large　portion　of　the　muriate　of　silver　which　is　to　be　got　rid　of；　it　should　be　dipped　once　or　twice　in　the　hyposulphite　solution。　By　this　operation　the　muriate　which　lies　upon　the　lighter　parts　will　become　so　altered　in　its　nature　as　to　be　unchanged　by　light；　while　the　rest　remains　dark　as　before。

It　will　be　evident　from　the　nature　of　the　process；　that　the　lights　and　shadows　of　an　object　are　reversed。　　That　which　is　originally　opaque　will　intercept　the　light；　and　consequently　those　parts　of　the　photogenic　paper　will　be　least　influenced　by　light；　while　any　part　of　the　object　which　is　transparent；　by　admitting　the　light　through　it；　will　suffer　the　effect　to　be　greater　or　less　in　exact　proportion　to　its　degree　of　transparency。　The　object　wholly　intercepting　the　light　will　show　a　white　impression；　in　selecting；　for　example；　a　butterfly　for　an　object；　the　insect；　being　more　or　less　transparent；　leaves　a　proportionate　gradation　of　light　and　shade；　the　most　opaque　parts　showing　the　whitest。　It　may　be　said；　therefore；　that　this　is　not　natural；　and　in　order　to　obtain　a　true　pictureor；　as　it　is　termed；　a　positive　picture　we　must　place　our　first　acquired　photograph　upon　a　second　piece　of　photogenic　paper。　　Before　we　do　this；　however；　we　must　render　our　photograph　transparent；　otherwise　the　opacity　of　the　paper　will　mar　our　efforts。

To　accomplish　this　object；　the　back　of　the　paper　containing　the　negative；　or　first　acquired　photograph；　should　be　covered　with　white　or　virgin　wax。　This　may　be　done　by　scraping　the　wax　upon　the　paper；　and　then；　after　placing　it　between　two　other　pieces　of　paper；　passing　a　heated　iron　over　it。　The　picture；　being　thus　rendered　transparent；　should　now　be　applied　to　a　second　piece　of　photogenic　paper；　and　exposed；　in　the　manner　before　directed；　either　to　diffused　day…light　or　to　the　direct　rays　of　the　sun。　The　light　will　now　penetrate　the　white　parts；　and　the　second　photograph　be　the　reverse　of　the　first；　or　a　true　picture　of　the　original。

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　potassiu