Science and Art come together in Textile Dye, Yarn and Fiber Analysis.





























Science and Textiles

PDA Spectral Information and HPLC Dye Analysis

specPub3.GIF (4188 bytes)

Call Casey Reed @ 505-344-8492

Textiles are usually analyzed from an art history point of view.  Using stylistic elements and colors people make judgements about old textiles, but a multidisciplinary approach is possible.   Art history and science meet when objective dye, yarn and fiber evidence is combined with ethnology, historical dye, yarn, and fiber use, and technical analysis, and of course stylistic elements from art history studies. 

How is dye analysis accomplished or determined? 

(Various dye analysis methods are compared)

The spectral information (that is illustrated below) is used to identify the dye from a red scale insect called Cochineal using High Pressure Liquid Chromatography (HPLC), and the PDA (Photodiode Array Detector).  This detector utilizes diodes that receive specific light or are able to generate a signal from light frequencies 2nm apart.  There are 300 diodes 2nm apart so we can look at 600nm of different light frequency.  The spectra above is from the detector tuned to 200nm to 600nm.  The high points on a graph represent intensity and the bottom line represents frequency. 

The PDA is tuned from 200nm to 800nm for indigoid testing, and adjusted for 200nm to 600nm for most other dyes.  Data or spectras are illustrated below in (fig. 1 Spectral Referencing - Standards-). 

The image and table at the bottom left (fig. 1) is an image from one of the computerized libraries standards - a dye component spectra (carminic acid), but this standard is also superimposed over one of the sample's spectra from the dye found in a yarn of raveled wool that was with another raveled wool yarn.  Four of the standard spectras of Cochineal's carminic acid matched in (fig. 1 left side ) with the sample of dye from the raveled yarn's spectra, which is the larger peak in the chromatograph in (fig. 2 right side).  Both samples were from a hand twisted raveled (machine z-spun) with a (machine s-spun) yarn to form a 2-ply yarn. 

Each of the raveled yarns had different dyes. The dominant quantity of dye indicated by the large peaks in (fig. 2 left side) are synthetic orange dye spectras.  

The comparison with the published spectra on the right is to illustrate how a standard in one method's spectral read out on cochineal in Brussels, Belgium by Jan Wouters can be compared to the read out obtained and established in a computerized library here in New Mexico, United States of America.   Both labs identified the same component "ca" (Carminic Acid) the main dye component in American Cochineal (dactylopius coccus costa), and in Armenian Cochineal (Prophyrophora hamelii), and in Polish Cochineal (Porphyrophora polonica).  These different forms of cochineal can be identified by quantifying different dye components spectrally identified on a chromatograph.   We make peak area comparison with the same identified dye component peaks in each of the chromatographs say in American cochineal and Armenian cochineal.  The peak areas on each chromatograph are consistent and comparable.   This gives us the evidence for the type of cochineal identification. 

The real advantage of the PDA and HPLC is one can identify peaks that may co-elute and separate mixtures.   It is also possible to view the detector's data from different frequencies and all the associated spectral data with each peak. 

The detector was tuned to 274nm for all of the spectral graphics and chromatographic illustrations in (fig. 1 to fig. 3) below.

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Carminic acid spectral data from the computerized library of 4 standards  superimposed on the sample  of dye from the large peak on the chromatograph in figure 3 below.  Produced by Casey Reed in Albuquerque New Mexico 1996.


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Cochineal's main dye component Carminic acid.   Spectra from  The Scale Insect Dyes (Homoptera: Coccoidea).   Species Recognition by HPLC and Diode-Array Analysis of the Dyestuffs.   By Dr. Jan Wouters and Andre Verhecken. 1989b. -  Belgium


fig. 1, Spectra Reference - Standards - from our computerized library in New Mexico on the left side compared to spectral data from a yarn sample. Spectral referencing standard from published material from the Annales de la Societe Entomologique de France 25(4):393-410, on the right side. 



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fig. 2,  Chromatograph of one red yarn divided and tested separately.  The one above shows large peaks as synthetic dye, and small peaks as a slight cochineal contamination on the left side of the figure. fig. 3,  The second peak on the left shows a large peak from Cochineal (carminic acid as in the spectral identification in fig. 1) and it's dye components as well as small peaks on the right side of the figure as contamination from the synthetic dye.


    These chromatographs and spectral data in (fig. 2) and (fig. 3) show how dyes can be separated and identified.   We separated these yarns based on microscopic evidence.   The dye analysis proceeded with the hypothesis that there were different yarn sources and possibly different dyes from observing the respective z-spun and s-spun yarns.   The results supported the prediction.   The results also show contamination from one yarn to the other.

All this data is mathematically based.  The areas of the peaks are calculated and compared as a total and each peak that represents a dye component can be represented as a percentage of the total peaks with identifiable spectras.  This allows qualitative and quantitative analysis of dyes found in tested yarns.  The time of elution is also critical to compound identification or the time of the peak's occurrence on the chromatograph.  When this elution time and chromatographic evidence is combined with spectral evidence from  the computer library, they work together to form the best way to identify dyes using toady's computerized technology. 

The microscopic analysis of yarns and fibers is the precursor to successful dye analysis because visual clues allow hypothesis building and follow up with HPLC dye analysis.   There are many other benefits to the microscopic analysis.  No visual damage occurs when the samples are taken from the textile.  It can be re-woven under the microscope and even a well trained eye typically can not find the point of intervention and extraction of samples. 

Fibers are identified using fiber standards including Camel, Goat, Churro wool, flax or linen, Silk, cotton, and dozens of other fibers found in textiles.  Visual identification is documented with microphotographic comparisons at 200x to 400x of standards and samples as the evidence for fiber identification.


Call Casey Reed  @  505-344-8492