JAIC 1989, Volume 28, Number 2, Article 3 (pp. 79 to 96)
JAIC online
Journal of the American Institute for Conservation
JAIC 1989, Volume 28, Number 2, Article 3 (pp. 79 to 96)


Elizabeth Estabrook


4.1 Visual Examination

4.1.1 Abrasion or Alteration of Cotton Surface

AFTER HAVING BEEN AGED for seven days the samples did not appear to have been abraded any more than before. That is, the abrasion of A samples was indistinguishable from that on B, C, D or E samples (see table 3).

Table 3 Alteration/Abrasion Of Cotton Duck and Quantity of Eraser Residue

  • Absorene: The fibers protruding from the yarn are redirected so that they are preferentially aligned in the direction of eraser and vacuum use.
  • Art Gum: As with Absorene.
  • Tapeten Reiniger: As with Absorene.
  • Pink Pearl: The fibers are redirected and some pulled out of the yarn. Crumbs are visible twisted and wrapped in cotton fibers.
  • Mars Plastic: as with Pink Pearl.
  • Magic Rub: as with Pink Pearl.
  • Kneaded Rubber: The fibers are altered in direction and some appear to have been pulled out of the yarn.

The severity of fiber redirection is clearly a function of the pressure applied during eraser use and of the firmness and density of the eraser itself.

4.2 Characterization of Crumbs

The quantity of crumbs was defined in the following manner: none; few (1 to 3 crumbs per cotton strip); moderate (4 to 6 crumbs); many (7 to 20); and abundant (21 or more). Tenacity was defined in the following manner: not tenacious (95%–100% crumbs had been removed after vacuuming); slightly tenacious (25% or fewer crumbs remained), and tenacious (75% or more crumbs remained). Other categories were not found to be necessary.

Absorene: The vacuumed samples have many crumbs, while the unvacuumed samples have an abundant quantity of crumbs. These particles are generally small, pale pink, and invisible to the unaided eye; the larger ones are darker in color and more easily seen. As the textile ages, they became darker and yellower. The particles tend to be in the fibers that stand proud of the weave, except if too much pressure has been used in applying the eraser. In that case, the residue is enmeshed in the weave itself. Crumbs on samples of all ages were easily disengaged from the fibers by several passes of a bristle brush. (The brushing action realigned the fibers but did not appear to alter the cotton in any other way.)

Art Gum: Many crumbs are left on the sample even after vacuuming. Without vacuuming, the crumbs are abundant. They are small, pale yellow, and difficult to see, even with magnification. With aging, they darken. The crumbs remaining on the surface after vacuuming tend to be deep in the weave of the textile rather than caught in the protruding fibers. However, they are easily removed by further vacuuming or bushing.

Tapeten Reiniger: There are a moderate number of crumbs on the samples that had been vacuumed and abundant crumbs on those that had not. The particles are very small and pale when fresh but darken to a deep orange upon aging. They are invisible to the eye unless present in large numbers. A bristle brush easily dislodges them; however, they can readily be redeposited if they are not removed from the brush hairs.

Pink Pearl: There are abundant small pink crumbs on the vacuumed samples. They become darker and yellower with age but are generally invisible to the eye. On the unvacuumed samples, larger curls of eraser residue are visible. Crumbs are visible both deep in the weave and in the fibers. They are tenacious and are not all removed even with aggressive brushing.

Mars Plastic: Few particles are visible on the vacuumed strips. Abundant, very tiny white crumbs are visible on the unvacuumed samples. They are mostly in the weave and invisible to the eye. Persistent brushing is necessary to remove them due to their quantity and location.

Magic Rub: There is a moderate number of crumbs on the vacuumed samples. These are small, rounded, white particles that are invisible to the eye. They do not discolor upon ageing. Unvacuumed samples contain larger particles that are caught in the fibers and slightly resistant to removal by brushing.

Kneaded Rubber: No crumbs are visible on the vacuumed strips; many are visible on the unvacuumed ones. The tiny transparent or white crumbs are invisible to the eye. They are mostly located in the weave and are easily brushed away.

4.3 Surface pH and Cold Extraction pH

No conclusions from the surface pH readings of the treated and untreated samples could be drawn as the results were not deemed scientifically significant. The pH measure for the textile fluctuated with the slightest change in the pH of the distilled water. In addition, the reading was dependent upon whether or not the droplet of water came into contact with and solubilized an eraser crumb. The results, therefore, have not been described here.

Surface pH measurements were taken of the erasers themselves. The results are shown in table 4. Cold extraction pH readings taken of the eraser crumbs are also shown.30

Table 4 Surface pH and Cold Extraction pH of Erasers

4.4 Tristimulus Values

Tristimulus values were obtained for each sample. The values correspond to the following: L = lightness (100) to darkness (0); a = red-green difference, with +a indicating redness while −a indicates greenness; b = blue-yellow difference, with +b indicating yellowness while −b indicates blueness. The values for a and b are zero for neutral colors such as gray, black, or white; however, their values rise as the color becomes more chromatic or saturated (see table 5).

Table 5 Tristimulus Values

Both primary and secondary illuminants were north sky daylight. In order to assess the effect of this choice as opposed to incandescent or cool white fluorescent, measurements were made on the same sample (10A) under each lighting condition. The results (see table 6), show that the illuminants affect the “L,” “a,” and “b” values in the following manner: Northern daylight gives the darkest, greenest, and least yellow values. Incandescent gives the middle value for lightness of these illuminants, the reddest and the middle value for yellowness. Cool white fluorescent gives the darkest and yellowest values as well as a neutral zone value for red-green. In table 7, the erasers are arranged in descending order from lightness to darkness, from −a to +a and from −b to +b to assess easily the effect of the erasers in relation to each other.

Table 6 Effect of Illuminants on Untreated Cotton

Table 7 Relative Tristimulus Values for E Samples

4.5 Brightness Measurements

Brightness measurements correspond to the light reflected from the sample at 457nm. Readings were taken for sample 10A in three different positions (horizontal, vertical, and diagonal) to determine the effect of weave direction on the brightness measurement. The change in value due to the direction of the weave was found to be insignificant, especially when compared to that caused by the eraser treatment.

Brightness values for the samples are shown in table 8. Table 9 lists the erasers in order, from those having the least to those having the greatest dulling effect on the brightness of the cotton sample.

Table 8 Brightness Measurements

Table 9 Realtive Brightness of Samples

The overall effect on the brightness of the cotton from B to E aging periods and in vacuumed and unvacuumed states was calculated by giving each eraser a ranking under each experimental condition. For example, in the B, unvacuumed state, the erasers are ranked as follows: Tapeten Reiniger (1), Art Gum (2), Absorene (3), Mars Plastic (4), Magic Rub (5), Pink Pearl (6), and Kneaded Rubber (7) (see table 9). Similar lists were compiled for each experimental variable, and the numbers ascribed to an individual eraser were added. The overall ranking appears in the far right column: The smallest number shows the eraser with the least dulling effect, while the highest number represents that product with the greatest effect.

Copyright � 1989 American Institute for Conservation of Historic and Artistic Works