After the last blog detailing the long awaited fruits of TF1 two issues were brought forward. The first was whether or not the casting artifacts present were due to surface action (i.e. dessication) or whether they were due to an error in mixing that resulted in air being trapped in the slurry. The second was what practical steps a person could take in order to prevent these types of artifacts from appearing. Fortunately for you (and me) these are two birds that are easily killed with one stone. In fact, you don't even need a whole stone. You could just use a pebble. You wouldn't even have to throw in that hard.
The importance of the first casting is not only that it demonstrates the types of artifacts that can occur, but it also provides a control. Without a control proper subsequent testing cannot take place. However, with this control in place we can not only test the hypothesis that artifacts are caused by surface action and not mixing but also easily demonstrate how to avoid them.
First things first we need to create another print to cast.
Note that in this impression several small pressure fractures were created along the surface of the print. Again these are often telltale signs of a ridged foot being impressed into a surface. For this test these impressions were left in place in order to provide an example of what this feature looks like on a cast track.
Again prior to moving on to the casting process the temperatures of the water (54 degrees F), ash (65 degress F), and plaster (65 degrees F) were noted. The room temperature was 68 degrees F and the relative humidity was 34 percent.In order to test the hypothesis that casting artifacts are indeed a result of surface action (and to show how they can be avoided) a barrier spray was used on the print. For this test I had originally planned on using an aerosol fixative designed for preserving graphite and charcoal drawings but at the last minute settled on using an aerosol hairspray. Three coats of hair spray were applied to the print. Each coat was applied at a height of 6" and allowed to cure for 15 minutes.
With the barrier spray in place the slurry was prepared. The plaster for this test was again mixed per the manufacturer's suggestion. 1200ml of plaster were added to 600ml of water and mixed by hand. As soon as the slurry was properly mixed it was poured directly into the center of the cast at a similar height and pour rate as the first test cast.
The slurry was once again given one hour to harden. During this time the same binding/fissuring action was noted along the rim of the print.
After setting for one hour the cast was removed from the ash. The cast was allowed 24 hours to set before being cleaned.
The below photo is of the first test cast for comparison.
One small artifact was observed bisecting the heel of the foot. The below photos are comparisons of the second test casting versus the first.
The point of impact of the slurry (bulls eye), deep multiple furrows, and adjoining dessication ridges abutting the furrows were all absent.
The casting did however capture much of the fine detail present in the track, including the pressure fractures noted earlier.
The results are quite clear. By following the same procedures as the test cast (control) and introducing the use of the barrier spray the casting artifacts have been virtually eliminated. Had the artifacts not been the result of surface action this would not have been the case as the barrier spray would have had not impact. This also illustrates how a person in the field or at home can easily solve this problem with the use of a simple household item.
