IR spectroscopy indicates higher
molecular degradation in organic historical paints after exposure to
pollutants By: ãInfectious Diseasesä Tara Dell Andrew Krieger Elise Chom
Discussion
Written by: Elise Chom
Revisions: Tara Dell and Andrew Krieger
Final Revisions: Tara Dell, Andrew Krieger, and Elise Chom
Through
experimentation, we compared two historical paint mediums with two modern
paints used today.Ê An experiment was
designed using modern acrylic, oil based, and egg
tempera mediums.Ê The historic oil based
and egg tempera paints were hand made according to their original recipe and
pigmented using dried
The Gladiolus petals used to pigment the historical paints of this investigation were organically derived. On the basis of previous research, it is known that organic compounds are more susceptible to biological degradation (Thom, 1975).Ê Additionally, it is recognized that few organic compounds are industrially produced (Thom, 1975).Ê The modern paints used in the experiment were industrially manufactured by the Behr Paint Company.Ê Based on these assumptions, multiple carbohydrate tests were performed to confirm the presence of several specific organic sugars.Ê Positive results for organic sugars in the historical paints would imply a greater susceptibility to pollutants.
ÊÊÊÊÊÊÊÊÊÊÊ A Benedictâs test was used to test for the presence of a free aldehyde or ketone group.Ê It was predicted that the acrylic paint would contain neither a free aldehyde nor a ketone group.Ê Conversely, it was believed that the tempera and walnut oil mediums would both test positive. Rationalization for this prediction relied on the fact that raw egg yolks and walnuts contain approximately 0.44g and 0.10g of glucose per cup (Fantasia, 2006).Ê Glucoseâs structure contains a free aldehyde.Ê Surprisingly, experimental data suggested that only walnut oil paint contained a free aldehyde or ketone.Ê This was indicated by a dark red color change after approximately three minutes of heating.Ê The egg tempera and modern paints A & B remained a blue color, indicative of a negative result.Ê
The Barfoedâs and Selivanoffâs test produced experimental results similar to the findings of the Benedictâs test.Ê The Barfoedâs test was used to determine whether each paint sample contained monosaccharides or di/polysaccharides.Ê We predicted the Barfoedâs test would reveal monosaccharides as the dominant form of sugars in the egg tempera paint and di/polysaccharides as the dominant form of sugars in walnut oil paint.Ê This prediction is based upon the fact that one cup of raw egg yolk contains approximately 0.44g of glucose and 0.17g of fructose while one cup of walnuts contains on average 2.92g of sucrose (Fantasia, 2006). Selivanoffâs test, which tested for the presence of ketoses and aldoses, was predicted to reveal the presence of aldoses in the egg tempera paint.Ê The walnut oil paint was expected to produce a disaccharide intermediate.Ê Experimental data indicates modern paint and egg tempera results revealed negative results, and the presence of a ketose in the walnut oil paint medium, and negative results for the egg tempera and modern paints A & B.Ê
The Bialâs test tested for the presence of a pentose or hexose furanose ring.Ê It was originally predicted that hexose furanoses would be detected in the walnut oil and egg tempera paints.Ê This prediction was based on the fact that walnuts and raw egg yolks contain 0.11g/cup and 0.17g/cup of the sugar fructose respectively (Fantasia, 2006).Ê Additionally, it was predicted that the modern paints would have neither ring.Ê These hypotheses were incorrect.Ê All paint samples tested underwent no color change, indicating that the walnut oil, egg tempera, and modern paints A & B contained neither a pentose or hexose furanose.Ê Lastly, an iodine test was utilized to identify the presence of starch. The experimental data confirmed the hypothesis that no starch was present in any paint sample.
Results from carbohydrate tests indicate that the egg tempera and modern paint mediums contained no carbohydrates detectable through our methods.Ê Conversely, walnut oil paint was determined to contain fructose.Ê Fructose was chosen as the most likely sugar because it contains a free aldehyde or ketone, a ketose, and is a reducing sugar monosaccharide.Ê Possible sources of error may involve our choice of paint color, red.Ê Many of the carbohydrate tests involved a red color change and it was difficult to see if the solution actually changed color.Ê This may have been avoided by using a different flower for pigmentation.
To test for
protein in each paint, a
ÊÊÊÊÊÊÊÊÊÊÊ Pigment differences were tested for using a Thin-Layer Chromatography (TLC).Ê Egg tempera and walnut oil paints were compared against each other as well as their matching modern counterpart.Ê Based on previous research, it was predicted that the tempera and walnut oil paints would both contain anthocyanins, a reddish/purple flavonoid.Ê It was also predicted that the modern paints would be much different than the historical in pigment composition.ÊÊÊ After experimentation, pigment differentiation could not be accomplished.Ê Using a mobile phase of 70%hexane and 30%acetone, Gladiolus pigmented walnut oil would not separate across the TLC strip (Figure 22).Ê One trial indicated a slight movement of a purple/red pigment, but no Rf value was obtained because the pigment failed to migrate to an adequate line, leaving vague small streaks across the bottom of the strip.ÊÊ One might argue that this is because the paint did not have an even consistency.Ê To address this problem, paint samples were prepared at 50% concentration and 100% concentration.Ê A sample of 75% paint and 25%acetone solution was also tested.Ê Results were still inconclusive with no attainable Rf value.Ê Believing that the mobile phase may be inadequate, another mobile phase of Gemini Masterpiece Odorless Paint Thinner was tested.Ê No pigment migration was obtained.ÊÊ It is still believed that this paint contained anthocyanin pigments based on previous research where they were isolated in Gladiolus petals (Takemure et al. 2005)
Egg tempera was pigmented with the same Gladiolus petals as the walnut oil paint.Ê For this reason, it was predicted that the same anthocyanins would be isolated in this paint as were in the walnut oil paint.Ê Similar vague streaks and unattainable Rf values were achieved as in the walnut oil paint.Ê Samples of 50% concentration, 100% concentration and acetone mixed were used.Ê Mobile phases of hexane and acetone and Gemini Masterpiece Odorless Paint Thinner were tested.Ê In each trial, similar results ensued and no conclusive Rf values were obtained.Ê Based on previous research where anthocyanins were isolated in Gladiolus petals, it is still believed that this paint does contain anthocyanin pigments (Takemura et al. 2005).Ê
When TLC was performed on modern paints A and B, zero migration occurred.Ê Originally it was believed that the paint was too concentrated.Ê To solve this problem paint was diluted to a 50% concentration.Ê These trials yielded zero migration.Ê When the paint samples were centrifuged, pigment and unidentifiable solid particles concentrated in the bottom of the cuvette.Ê This sample was used but still yielded zero migration.Ê Believing that the mobile phase was an inadequate solvent, Gemini Masterpiece Odorless Paint Thinner was used to try to separate pigments.Ê No adequate migration ensued.Ê We believe that the pigments were too bound up in polymers to migrate with the solvent. Latex polymers often emulsify water paint used today (Columbia Encyclopedia, 2001).ÊÊÊ
ÊÊÊÊÊÊÊÊÊÊÊ A final assay was conducted to compare the molecular degradation between each paint sample after exposure to environmental pollutants. For the purpose of this experiment, molecular degradation will be defined as any change in the molecular structure of the paint sample.Ê Smoke used was meant to simulate soot from the combustion of fuel sources.Ê Soot is known to be detrimental to artwork. Buildup over time produces a fine layer which absorbs light normally reflected by the paintâs surface (Salmon et al., 2000).Ê Vaporized sulfuric acid was used to simulate sulfur in the atmosphere.Ê Sulfur is a common byproduct of industrial manufacturing.
Each paint was exposed to smoke from a burning newspaper and vaporized 3.5M sulfuric acid.Ê An IR spectrometer was used to analyze molecular structures before and after exposure to the pollutants.Ê Previous research has revealed the presence of anthocyanins in the petals of Gladiolus (Takemura et al, 2005).Ê Anthocyanins are known to be unstable to physical and chemical changes (Harborne, 1993).Ê Because Gladiolus petals were used to pigment the historical paints, it was the pigments of these paints would show greater signs of degradation.Ê It was also predicted that the modern paints would remain relatively unchanged.ÊÊ When post exposure Infrared spectrums were compared to pre-exposure infrared spectrums predictions were confirmed.Ê Both the modern paint A and B produced almost identical spectrums before and after exposure (Figure 27, Figure 28).Ê
The paint with the most change in molecular structure was the walnut oil paint.Ê After exposure the spectrum revealed several new chemical bonds including a secondary alcohol, a secondary amine, a fluoroalkane, and a chloroalkane (Table 9).Ê We believe that soot particles may have adhered to the moist surface of the oil based paint, appearing to alter the chemical structure.Ê If this were the case the changes visible to the IR spectrometer would be a direct result of the soot particles instead of the paint.Ê This is supported by the fact the readings taken from the IR spectrometer are very surface sensitive.Ê Egg tempera paint showed fewer differences in its infrared spectrum after exposure to pollutants than did the walnut oil paint.Ê Changes in the molecular structure of the egg tempera paint, producing an alkyne and shifting a secondary alcohol to a primary alcohol (Table 10).Ê
As the protein and carbohydrate tests indicated, egg tempera and walnut oil contain organic components.Ê It is recognized that organic compounds are susceptible to biological degradation (Thom, 1975).Ê This would explain the changes in molecular structures.Ê Since there were no changes in molecular structure of both modern paints A and B, no degradation was noted.Ê The modern paints resisted the environmental pollutants better than the historical paints.
The modern paints of today truly do hold their color better than historical methods of egg tempera and walnut oil medium paints.Ê This was expected because of the purposes of modern paints.Ê People want paint that will withhold the test of time. (Krieger, 2006)Ê While the modern paints last significantly longer, egg tempera and walnut oil paints are beautiful in their own respect and will always be appreciated in timeless Renaissance pieces.
Future Directions
This investigation is only a small piece of a larger puzzle of art history. Many improvements could be made throughout the procedures.Ê In order to improve the carbohydrate tests, a larger variety of experiments could be performed.Ê This would provide a more detailed and thorough investigation of the individual macromolecules in the paints being tested.Ê Results would provide a more meaningful analysis of current data and allow for a broader connection to outside research.ÊÊ Also a larger sample size of historical and modern paints would provide a more thorough investigation.Ê Additionally, experimenters must be mindful of the colors of paint sample chosen with attention to color dependent reactions.Ê In some of our carbohydrate experiments, it was difficult to determine if the solution changed color due to a positive result or if it was simply the color of the paint.ÊÊ This could have been avoided by staying away from red, yellow, and green paint and by not using a red pigment.ÊÊ
To improve the
The Thin Layer Chromatography assay failed completely.ÊÊÊ Little or no conclusive results were found for any of the paints in each of the different trials.Ê The assay failed because inadequate solvents were used for the mobile phase.Ê To combat this, a proper mobile phase would have to be found for each of the paints.Ê For the synthetic modern paint, it would have to be determined if the paint was completely inorganic.Ê If the paint was found to be completely inorganic, then a solvent that could pull pigment from a polymer could be used.Ê For the historical paints one should use a solvent capable of adequately separating and migrating pigments.Ê The 70% hexane 30% acetone mobile phase wasÊ not completely successful in separating pigments, thus no Rf values could be measured and not pigments conclusively determined.
Ê Experimenting with a wider variety of environmental pollutants could improve the third assay. In this experiment sulfuric acid was used to represent sulfur in the atmosphere.Ê However, nitric oxide is another pollutant that should be looked into.ÊÊ Nitric oxide was not used in this experiment because of its high cost and difficulty to obtain.
Overall, this study has provided useful insight into the larger issue at hand.Ê Many questions still remain unanswered.Ê Research along these lines could aid in saving the priceless masterpieces that represent the essence of our culture.Ê Without the proper knowledge to protect our history, it could be lost forever.
