But while chrome yellow could easily have produced the color on the Longfellow gown, it is unlikely to be the cause. While early dye books suggest its use on silk (with potassium chromate), they also mention that it is not at all colorfast when washed. Research into later manuals suggests that dyers switched to potassium dichromate in order to improve fastness, but that the dichromate severely injured silk - to the point that it “[gave] it the appearance of cotton, on which account it is never used by experienced silk dyers." (Partridge, 98.) From the 1830s onward, chrome yellow was recommended only for use on calicos and some woolens.
In summation: Mrs. Longfellow’s dress was most likely dyed using either quercitron bark or picric acid. It was spot tested and found to be not entirely wash-fast; with soap, a very small amount of the yellow dye bleeds out. But it is relatively wash-fast, and a dress like that would generally not have been washed during its period of use, which is why it still appears so even and bright today.
We close out our series of three MTS Blogs on the subject of Fanny Appleton Longfellow's Spanish-style dress with an exploration of the synthetic dyes available in the 1850s.
If the color of the dress is not due to a natural dye, another potential material is the first of the coal-tar, or chemical, dyestuffs: picric acid. Its proper formulation was discovered in 1845, and factories existed for its production by at least 1855. Contemporary findings note that it was more colorfast than any of the vegetable dyes discussed previously, but subsequent research proved that it was not up to the standard of mineral and chemical alternatives. Despite this, it continued to be used throughout the nineteenth century on a variety of materials, and the vibrancy and purity of the color on this dress could be attributed to it.
Another option, aniline dyes, were both bright and colorfast, which made them extremely popular in a very short amount of time. Textile conservators at Museum Textile Services determined that the Longfellow yellow silk is colorfast in water, like an aniline dye. If it were dated to just a few years later, it could feasibly have been one of the first silks dyed this way; however Charles Mène’s "aniline yellow" was created in 1861, the same year that Fanny Appleton Longfellow died.
The last contemporary possibility is a mineral dye. At least one was in use for yellows by 1820: chrome yellow, which the modern reader will recognize as the color of American school buses. It comes from a mineral called crocoite, which was first discovered in the 1790s and is a standard paint color still used by modern artists. The French chemist Vauquelin began by synthesizing pigments from the mineral, and it took thirty years for a breakthrough on chemical dye use. By 1820, dyers were able to achieve a deep and striking yellow with lead chromate (a combination of lead acetate and either potassium chromate or dichromate). The name ‘chrome yellow’ derives from these chemical mordants rather than from appearance or a comparison to nature, and thus does not seem to have been used in fashion magazines like Godey’s and Peterson’s until much later in the century. In the 1850s, the brightest of chrome yellows were probably referred to as ‘canary’ or ‘sulphur’ yellows. The term ‘chrome yellow’ does appear occasionally, but only in reference to paint pigment for craft projects and home décor. It was a popular choice all around; within only a couple of years of its initial manufacture, George IV of England chose it to color the wallpaper of his Royal Pavilion in Brighton.
These articles have given a historical overview of the most likely dyestuffs; without in-depth analysis, it can be very difficult to tell what a fabric was colored with. Swatches can aid visual identification, but in a case like ours, where quercitron can create the same colors that weld can, there is an obvious difficulty. There are various techniques that are able to break this barrier, FTIR and mass spectrometry, but all require more resources than what we have at the MTS studio. Low tech, non-invasive dye identification is an area sparse in scholarship, and often historical research can be a conservator’s--and a curator's-- best bet.
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