the history and practice of the art of photography-第20章

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　in　about　ten　minutes；　it　must　then　be　removed；　washed　and　dried。　　By　this　process　the　picture　is　rendered　more　transparent；　and　its　lights　become　whiter。　It　is　also　rendered　exceedingly　permanent。　　After　this　process　the　picture　may　be　waxed；　and　thus　its　transparency　increased。　This　process　is　applicable　to　all　photographic　papers　prepared　with　solutions　of　silver。

Having　thus　fully；　and　it　is　hoped　clearly；　considered　the　process；　it　may　be　necessary　before　dismissing　the　calotype　from　notice；　to　add　one　or　two　remarks　from　the　observations　and　labors　of　some　who　have　experimented　in　this　art。　　Dr。　Ryan　in　his　lectures　before　the　Royal　Polytechnic　Institution；　has　observed；　that　in　the　iodizing　process　the　sensitiveness　of　the　paper　is　materially　injured　by　keeping　it　too　long　in　the　solution　of　iodide　of　potassium；　owing　to　the　newly　formed　iodide　of　silver　being　so　exceedingly　solvable　in　excess　of　iodide　of　potassium　as　in　a　few　minutes　to　be　completely　removed。　The　paper　should　he　dipped　in　the　solution　and　instantly　removed。　There　is　another　point；　too；　in　the　preparation　of　the　iodized　paper　in　which　suggestions　for　a　slight　deviation　from　Mr。　Talbot's　plan　have　been　made。　　In　the　first　instance；　it　is　recommended　that　the　paper　be　brushed　over　with　the　iodide　of　potassium；　instead　of　the　nitrate　of　silver；　transposing；　in　fact；　the　application　of　the　first　two　solutions。　The　paper；　having　been　brushed　over　with　the　iodide　of　potassium　in　solution；　is　washed　in　distilled　water　and　dried。　It　is　then　brushed　over　with　nitrate　of　silver；　and　after　drying　is　dipped　for；　a　moment　in　a　fresh　solution　of　iodide　of　potassium　of　only　one…fourth　the　strength　of　the　first；　that　is　to　say；　one　hundred　and　twenty…five　grains　of　the　salt　to　a　pint　of　water。　　After　this　it　is　again　washed　and　dried。　The　advantage　derived　from　this　method；　is　a　more　sensitive　paper；　and　a　more　even　distribution　of　the　compounds　over　the　surface。

Another　deviation　from　Mr。　Talbot's　method　has　been　suggested；　as　follows：

Brush　the　paper　over　with　a　solution　of　one　hundred　grains　of　nitrate　of　silver　to　an　ounce　of　water。　　When　nearly；　but　not　quite；　dry；　dip　it　into　a　solution　of　twenty…five　grains　of　iodide　of　potassium　to　one　ounce　of　distilled　water；　drain　it；　wash　it　in　distilled　water　and　again　drain　it。　Now　brush　it　over　with　aceto…nitrate　of　silver；　made　by　dissolving　fifty　grains　of　nitrate　of　silver　in　one　ounce　of　distilled　water；　to　which　is　added　one　sixth　of　its　volume　of　strong　acetic　acid。　Dry　it　with　bibulous　paper；　and　it　is　ready　for　receiving　the　image。　When　the　impression　has　been　received；　which　will　require　from　one　to　five　minutes　according　to　the　state　of　the　weather；　it　must　be　washed　with　a　saturated　solution　of　gallic　acid　to　which　a　few　drops　of　the　aceto…nitrate　of　silver；　made　as　above；　have　been　added。　The　image　will　thus　be　gradually　brought　out；　and　may　be　fixed　with　hyposulphite　of　soda。　　To　obtain　the　positive　picture；　paper　must　be　used　brushed　over　with　an　ammonio…nitrate　of　silver；　made　thus：　forty　grains　of　nitrate　of　silver　is　to　be　dissolved　in　one　ounce　of　distilled　water；　and　liquid　ammonia　cautiously　added　till　it　re…dissolves　the　precipitate。

A　pleasing　effect　may　be　given　to　calotype；　or　indeed　to　all　photographic　pictures；　by　waxing　them　at　the　back；　and　mounting　them　on　white　paper；　or　if　colored　paper　be　used；　various　beautiful　tones　of　color　are　produced。

POSITIVE　CALOTYPE。

At　a　meeting　of　the　British　Association；　Professor　Grove　described　a　process　by　which　positive　calotype　pictures　could　be　directly　obtained；　and　thus　the　necessity　to　transfer　by　which　the　imperfections　of　the　paper　are　shown；　and　which　is　moreover　a　troublesome　and　tedious　process；　is　avoided。　As　light　favors　most　chemical　actions；　Mr。　Grove　was　led　to　believe　that　a　paper　darkened　by　the　sun　（which　darkening　is　supposed　to　result　from　the　precipitation　of　silver）　might　be　bleached　by　using　a　solvent　which　would　not　attack　the　silver　in　the　dark；　but　would　do　so　in　the　light。　The　plan　found　to　be　the　most　successful　is　as　follows：　ordinary　calotype　paper　is　darkened　till　it　assumes　a　deep　brown　color；　almost　amounting　to　black；　it　is　then　redipped　into　the　ordinary　solution　of　iodide　of　potassium；　and　dried。　When　required　for　use　it　is　drawn　over　dilute　nitric　acid　one　part　acid　to　two　and　a　half　parts　water。　　In　this　state；　those　parts　exposed　to　the　light　are　rapidly　bleached；　while　the　parts　not　exposed　remain　unchanged。　　It　is　fixed　by　washing　in　water；　and　subsequently　in　hyposulphite　of　soda；　or　bromide　of　potassium。

Mr。　Grove　also　describes　a　process　for　converting　a　negative　calotype　into　a　positive　one；　which　promises；　when　carried　out；　to　be　of　great　utility。

Let　an　ordinary　calotype　image　or　portrait　be　taken　in　the　camera；　and　developed　by　gallic　acid；　then　drawn　over　iodide　of　potassium　and　dilute　nitric　acid　and　exposed　to　full　sunshine；　while　bleaching　the　dark　parts；　the　light　is　redarkening　the　newly　precipitated　iodide　in　the　lighter　portions　and　thus　the　negative　picture　is　converted　into　a　positive　one。

The　calotype　process　has　been　applied　to　the　art　of　printing；　in　England；　but　it　possesses　no　advantages　whatever　over　the　method；　with　type；　now　so　gloriously　brought　to　perfection；　and　I　can　hardly　think　it　will　ever　be　made　of　any　utility。　For　the　benefit　of　the　curious；　however；　I　will　give　Mr。　Talbot's　method。

Some　pages　of　letter…press　are　taken　printed　on　one　side　only；　and　waxed；　to　render　them　more　transparent；　the　letters　are　then　cut　out　and　sorted。　To　compose　a　new　page　lines　are　ruled　on　a　sheet　of　white　paper；　and　the　words　are　formed　by　fixing　the　seperate　letters　in　their　proper　order。　The　page　being　ready；　a　negative　photograph　is　produced　from　it；　from　which　the　requisite　number　of　positive　photogenic　copies　may　be　obtained。

Another　method；　which　requires　the　use　of　the　camera；　consists　in　employing　large　letters　painted　on　rectangular　pieces　of　wood；　colored　white。　　These　are　arranged　in　lines　on　a　tablet　or　board；　by　slipping　them　into　grooves　which　keep　them　steady　and　upright；　thus　forming　a　page　on　an　enlarged　scale。　It　is　now　placed　before　a　camera；　and　a　reduced　image　of　it　of　the　required　size　is　thrown　upon　the　sensitive　paper。　The　adjustments　must　be　kept　invariable；　so　that　the　consecutive　pages　may　not　vary　from　one　another　in　the　size　of　the　type。　Mr。　Talbot　has　patented　his　process；　but　what　benefit　he　expects　to　derive　from　it；　I　am　at　a　loss　to　determine。

Enlarged　copies　of　calotype　or　Daguerreotype　portraits　may　be　obtained　by　throwing　magnified　images　of　them；　by　means　of　lenses；　upon　calotype　paper。

THE　CHRYSOTYPE。

A　modification　of　Mr。　Talbot's　process；　to　which　the　name　of　Chrysotype　was　given　by　its　discoverer；　Sir　John　Herschel；　was　communicated　in　June　1843　to　the　Royal　Society；　by　that　distinguished　philosopher。　This　modification　would　appear　to　unite　the　simplicity　of　photography　with　all　the　distintness　and　clearness　of　calotype。　This　preparation　is　as　follows。

The　paper　is　to　be　washed　in　a　solution　of　ammonio…citrate　of　iron；　it　must　then　be　dried；　and　subsequently　brushed　over　with　a　solution　of　the　ferro…sesquicyanuret　of　potassium。　　This　paper；　when　dried　in　a　perfectly　dark　room；　is　ready　for　use　in　the　same　manner　as　if　otherwise　prepared；　the　image　being　subsequently　brought　out　by　any　neutral　solution　of　gold。　Such　was　the　first　declaration　of　his　discovery；　but　he　has　since　found　that　a　neutral　solution　of　silver　is　equally　useful　in　bringing　out　the　picture。　Photographic　pictures　taken　on　this　paper　are　distinguished　by　a　clearness　of　outline　foreign　to　all　other　methods。



CHAP。　X。

CYANOTYPEENERGIATYPECHROMATYPEANTHOTYPEAMPHITYPE　AND　〃CRAYON　DAGUERREOTYPE。〃


The　several　processes　enumerated　at　the　head　of　this　chapter；　are　all　discoveries　of　English　philosophers；　with　the　exception　of　the　third　and　last　named。　　Anthotype　was　first　attempted　by　M。　Ponton　a　French　savan；　although　it　was　reserved　to　Mr。　Hunt　to　bring　the　process　to　its　present　state。　The　〃Crayon　Daguerreotype〃　is　an　improvement　made　by　J。　A　Whipple；　Esq。；　of　Boston

I。　CYANOTYPE；

So　called　from　the　circumstance　of　cyanogen　in　its　combination