Unveiling the Colours of Cellulose Nitrate Black and White Film-based Negatives in Colonial Photography

Aiming at contributing to the preservation of black and white (B&W) film-based negatives held by Portuguese archives, four photographic collections from the first half of the twentieth century were selected for study. During the macro assessment of the collections the preservation condition and hues found in photographic negatives from the Elmano Cunha e Costa (ECC) were noticed, distinguishing this collection from the remaining ones. Additional attention was given considering that the ECC collection was formed in a colonial context in the 1930s, while the others were formed on the Portugal mainland. The ECC collection results from an ethnographic survey of Angolan tribes recorded with B&W film-based negatives. In this collection, sets of negatives with pink, lemon yellow, greenish, orange brownish, and red brownish hues were found. To identify the origin of such hues, the image layer was analysed by microscale energy-dispersive X-ray fluorescence (μ EDXRF) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX). Additionally, to assess the base decay and its effect on the formation of hues, the plastic supports were characterized by Fourier transform infrared microscopy (μ FTIR). To complement the assessment of the film-base decay, pH was measured by using combined microelectrodes. The identification of mercury, iodine, chromium, and iron by μ EDXRF allowed correlation of the hues found in the negatives with chemical corrective treatments performed to improve the image quality. SEM-EDX confirmed those results and proved that the elements found were in the photographic emulsion layer. The results obtained are relevant since the hues identified may now be used as markers to indicate the technical work performed on colonial photography. Additionally, the visual and molecular assessment of the negatives’ supports (good to fair condition) allow proposing that the original storage conditions may have had a beneficial contribution to their present condition.

为助力葡萄牙档案馆所藏黑白（B&W）胶片负片的保护工作，研究选取了20世纪上半叶的四组摄影藏品开展研究。在对藏品进行宏观评估期间，研究人员注意到埃尔马诺·库尼亚·达科斯塔（Elmano Cunha e Costa，简称ECC）藏品的负片保存状况与色调特征，使其区别于其余三组藏品。此外，鉴于ECC藏品形成于20世纪30年代的殖民语境中，而其余藏品均来自葡萄牙本土，研究对其予以额外关注。ECC藏品源自以黑白（B&W）胶片负片记录的安哥拉部落民族志调查。该藏品中发现了带有粉色、柠檬黄、偏绿、橙棕以及红棕色调的负片组。为明确此类色调的成因，研究通过微区能量色散X射线荧光光谱（μ EDXRF）与扫描电子显微镜-能量色散X射线能谱（SEM-EDX）对影像层开展分析。此外，为评估片基老化及其对色调形成的影响，研究通过傅里叶变换红外显微光谱（μ FTIR）对塑料片基进行表征分析。为补充评估胶片片基老化情况，研究采用复合微电极测量了样品的pH值。通过μ EDXRF检测出汞、碘、铬与铁元素，研究人员可将负片中发现的色调与为提升影像质量所实施的化学修复处理建立关联。SEM-EDX验证了上述结果，并证实检测到的元素均分布于摄影乳剂层中。本研究所得结果具有重要意义：本次鉴定出的色调可作为标识，用以反映殖民时期摄影作品所经历的技术处理流程。此外，对负片片基的视觉与分子表征评估结果显示（样品保存状态为良好至尚可），其原始存储条件或对当前的保存状态起到了积极作用。