吶喊為挪威畫家愛德華·孟克的作品,其呼喊的「怪異」樣貌形象非常鮮明。768Please respect copyright.PENANALhe4hGbBCb
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他本人在1893至1916年畫出多個版本,而其中一幅展示在孟克美術館(Munch Museum)的版本因多處黃色地方出現變白及脫落跡象關係(圖1的數字標記區域),自2006年起已甚少公開示人。768Please respect copyright.PENANAJynWZOejJw
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作品現時正處於光線陰淡、攝氏18度、相對濕度約50%的環境備受保護。768Please respect copyright.PENANAN8Mu32MJQP
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(圖2)為了解箇中顏料變色及脫落的機制,有科學家對吶喊作品作出深入研究,並在近日發表文章講述得出的結果(Ref1)。768Please respect copyright.PENANAjdy4c5BU1U
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Cadmium sulfide,為該時期常用作為黃色顏料的化學物。768Please respect copyright.PENANA2j9HGTTLcs
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同期的文森·梵谷 (Vincent van Gogh)、詹姆斯・恩索 (James Ensor)和亨利·馬諦斯(Henri Matisse)均有利用這種化學物所製成的顏料,而相關的作品亦有出現黃色顏料變白的現象。768Please respect copyright.PENANA2ZWKtF5aVQ
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該時期主要有兩種方式製作Cadmium sulfide,分別為Dry及Wet Method。768Please respect copyright.PENANAPRyuHRrKwT
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Dry Method為以300°C至600°C及零氧氣的方式,加上大量硫元素(Sulphur)調配Cadmium sulfide的方式,得出的成品相對上較為純正。768Please respect copyright.PENANAYphV93n4eO
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Wet Method為將不同的化學物混合在一起(如圖中所示),再以沉澱的方式獲取固體Cadmium sulfide。768Please respect copyright.PENANA4fpt7DTtcW
基於當時技術相對上不太先進,最終的產品會含有較多雜質及副產品。768Please respect copyright.PENANAKClz4Peas4
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(圖3)科學家在文中嘗試挖取微量的吶喊畫碎粒,再利用各種技術檢測畫中的化學物成份。768Please respect copyright.PENANAknpa03m557
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圖3中間的圖片,其紅點代表黃色顏料Cadmium sulfide的存在。768Please respect copyright.PENANAy8uW9pUXKh
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下方的圖片,其三種顏色的出現分別代表Wet Method的副產物。768Please respect copyright.PENANAqXDjC521c6
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紅點:Cd(OH)Cl768Please respect copyright.PENANAWoqjI7LGVO
綠點:CdSO4768Please respect copyright.PENANApW3fGdoNsM
藍點:CdCO3768Please respect copyright.PENANAZ2RtYuYmbQ
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這三種副產物,在長久而來的知識中已被確認是顏料變色及脫落的兇手,與吶喊作品所出現的現象不謀而合。768Please respect copyright.PENANAXGPFTqNUPZ
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(圖4)為進一步了解顏料變色的現象,他們找來了吶喊畫同期帶有黃色顏料的作品(他們已7914數字命名樣本)。768Please respect copyright.PENANAnRd9vRbUTQ
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拿取畫中碎片後,(圖4左方)他們同樣發現裡頭含有Wet Method的副產物(綠點)。768Please respect copyright.PENANA49idU7xrtf
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為了解環境因素對於顏料變色的影響,他們對另一塊畫碎用上90 日相對濕度≥ 95%,攝氏為40°C,無光環境來模仿歲月的摧殘。768Please respect copyright.PENANA0u5wF3SqQz
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他們發現得到Wet Method的副產物Cd(OH)Cl(綠點)數量大增且集中在一起,其目測得到黃色顏料變白的現象發生。768Please respect copyright.PENANAGyZZ5qkX6L
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然而,用上用上90 日相對濕度=45%,攝氏為30°C,300W光源直接照射的環境來模仿歲月摧殘的話,則沒有感測得到Wet Method副產物的產生和顏料變色現象發生。768Please respect copyright.PENANAaSaiN3Mk41
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(圖5)另外,他們亦對愛德華·孟克那時期捐贈予館舍的顏料油作出檢測。768Please respect copyright.PENANA4ue8z9sMjW
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在畫紙塗上顏料油後,已能測量得到有一定程度份量的Wet Method副產物Cd(OH)Cl(左圖綠點)。768Please respect copyright.PENANAX649hZVUsy
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(右圖)用上90 日相對濕度≥ 95%,攝氏為40°C的方式摧殘後,綠點數量大增且集中在一起。768Please respect copyright.PENANAW7hTcUiuFP
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(圖6)換句話說,當時期以Wet Method製作的Cadmium sulfide顏料以及愛德華·孟克所使用的顏料油,乃是導致畫中黃色地方出現變白及有脫落跡象的元兇,而其變色的機制主要由相對濕度和溫度而非光線控制。768Please respect copyright.PENANA3vsGQHCEB1
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基於這發現,在相對濕度及溫度嚴密的控制下,吶喊他日將來也許會有機會可以再度長期公開示人。768Please respect copyright.PENANA6AbPeIvpyu
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Ref1:https://advances.sciencemag.org/content/6/20/eaay3514768Please respect copyright.PENANAwksT4N7i5H