5 DISCUSSION

5.1 Visual Examination

THE QUANTITY AND HENCE THE EFFECT of the eraser crumbs left on the cotton is an important factor especially when they are tenacious and cannot be thoroughly removed. The most tenacious crumbs proved to be those of Pink Pearl. The vinyl eraser crumbs were only slightly better. Others were easily removed provided the eraser had not initially been used with excessive force. (This is especially true of Absorene.)

The quantity of crumbs is a particular concern when they are invisible to the eye and therefore appear to have been removed without actually being so. Even after vacuuming, many crumbs were left by Absorene, Art Gum, and Pink Pearl, while few or none were left by Mars Plastic and Kneaded Rubber. However, these last two—along with Magic Rub and Pink Pearl—altered the surface the most. Absorene, Tapeten Reiniger and Art Gum altered it the least.

5.2 Surface pH and Cold Extraction pH

Results from the surface pH and cold extraction pH measurements of the erasers show a broad range: Absorene is the most acidic, while Art Gum is the most alkaline. However, the differences in the eraser pH did not have a measurable effect on the pH of the cotton samples in this experiment.

Because of the discrepancy between the surface pH and the cold extraction pH values obtained for Art Gum, a small experiment was undertaken. The eraser was cut along the short axis into four parts. The surface pH of each interior surface and of the exterior surfaces was taken. The results showed a large variation between the pH of interior and exterior surfaces. Readings taken sixteen days later on the same eraser showed a decrease for the interior pH values. The general explanation for this must be that acidic degradation products from as the eraser oxidizes, however, the specific reaction is unclear.

5.3 Tristimulus Values

The tristimulus values show that in most values, L, a, and b, Art Gum, Absorene, and Tapeten Reiniger consistently gave the best results, affecting the lightness, redness, and yellowness the least even after ageing. Pink Pearl and Kneaded Rubber, on the other hand, gave the worst results, causing the greatest change in these values.

Pink Pearl gave an especially high value for redness due to the eraser color and the quantity of residue left on the cotton surface. The vinyl erasers gave moderate values in each category.

5.4 Brightness Measurements

Art Gum, Absorene and Tapeten Reiniger affect the brightness of the cotton the least. Kneaded Rubber and Pink Pearl have the greatest and most immediate effect; the values have already dropped by 2 or 3 units, when compared to the control sample, in the B stage of aging and continued to dull the fabric as the aging progressed.