Making an Artificial Rock, Part II by Dierk Neugebauer I concluded last month's issue with the completion of the rock mold made out of fiberglass. In this issue I will describe the actual process of using this mold to create a light weight fiberglass rock suitable for bonsai planting. Having made sure that the mold had no parts that were "undercut" or otherwise defective, I then proceded to begin the rock casting. First of all, I coated the inside of the mold with the special mold release wax that I had purchased from my fiberglass supplier. This job was easier said than done, since the surface of the mold had naturally picked up the texture of the rock, and was, therefore, rather rough in spots. However, with a little perseverence, the job got done, and the wax was polished as much as possible. Next came a good application of the liquid mold release. Just as before, this was now applied to the inside of the mold. In places where the wax was particularly shiny (there were very few of these), the liquid tended to separate, but that was to be expected, and would not cause further problems. Once the mold was completely dry on the inside, I was ready to begin applying what I expected to be the final colour of my artificial rock. That sounds strange, but the process of working with a mold is to begin by applying the final surface of whatever object is being molded, and then adding the background support to the paint, so to speak. You will recall that I had purchased some small quantities of gellcoat (fiberglass paint intended for use in fiberglass molds):white, black, red, and blue. I took several small plastic yogurt containers, and added these colors singly and in combination to each container: in one I mixed black and white to get grey; in another blue and red for a dark purple. The challenge here was to apply these colours, one at a time, in such a way that they would imitate the surface of a rock. This proved to be easier said than done. I carefully prepared my little recycled yogurt containers with the various colours of resin in them. They all needed the catalyst added at the same time, so speed was of the essence. When working with a mold, the first thing that is applied to its inside is the final colour of the object being created. Here you see several colours in the mold, before the fiberglass application began. The first colour I chose to work with was grey. I mixed a few drops of hardener with the paint and applied it irregularly over the inside of the mold. Next came some dark purple which was soon followed by black and eventually some white. Here's where the fun began. When I picked up the container of black to mix the hardener with it, the container sprung a leak and spilled a fair bit of gellcoat paint on the table. As if that wasn't bad enough, the white container lost its bottom just as I was holding it over the mold. You can imagine the mess! Fortunately most of that white paint would not be seen since earlier applied colours had already covered most of the inside of the mold. Once this painting was finished and the paint had hardened, it was time to apply one or two backup layers of fiberglass matting. The procedure here was the same as in the making of the original mold: cut the matting into small pieces (the smaller the better), saturate with resin to which hardener had been added, and dab into place inside the mold with the aid of a stiff paint brush. I made sure that I had added a little black gellcoat paint to the resin so that it would be impervious to light if any parts were not covered with gellcoat paint. I had originally planned to curve the bottom edge of the rock inwards, so that it looked to have more substance to it, but found this task impossible to achieve: if the matting adhered to the lower part of the mold, I could then not fold it in towards the middle of the mold without pulling it away from the mold wall; thus creating a smooth round bottom edge on the rock was not possible as I had originally envisioned it. I decided to deal with this difficulty later, once the fiberglass rock had been removed from the mold. I had some misgivings about my rock releasing easily from its mold, and so I did not want to apply too much matting. I reasoned that the less matting there was, the more flexibility, and the easier to remove the rock from the mold, should it resist. I was correct: removing the rock casting proved to be a significant challenge! Once again the trusty screwdriver was needed to pry the wall of the rock from the inside of the mold. But the rock would not come out! Next pliers came to the rescue as I attempted to pull the rock out with them. Finally while using the screwdriver to apply some leverage, the mold released its hold, and a rock was born. ... For the first time I could see what my initial rock painting looked like. A thing of beauty it was definitely not! The colours were garish and unnatural, and several gaps appeared where the matting had not taken on the shape of the mold itself, probably due to some captured air bubbles that I had not successfully worked out when applying the fiberglass matting. In other places the gellcoat paint had lifted since it had no matting behind it to support it. The bottom of edge of the rock casting was rough, ragged and very unnatural looking. Once I had recovered from this disappointment I decided to salvage as best I could, my creation. First I used a pair of sheet metal sheers to trim the rough bottom edges so that it looked a little more level, as if the rock had been sliced in two. This wasn't what I originally had in mind, but a compromise was needed. I decided that the surface of the rock needed to be toned down as well. I mixed some more grey gellcoat with resin and hardener, and applied the same to most of the outer face of the rock. Then, before the gellcoat had a chance to harden, I took some clean, dry, concrete sand and sprinkled that over the rock, on the expectation that some of it would adhere to the rock once the gellcoat had hardened. Removing the newly minted rock from the mold proved to be quite a challenge, but I persisted. The new rock after some resin and colour adjustments have been made to "naturalize" it a little more. Once dry, I cleaned off the loose sand, and admired my handiwork. It was not the rock I had imagined I would create. It did not reflect the finer details of the original rock that I had used to make the mold. But despite this, it seemed that it could indeed function very nicely as a bonsai container. ... and it was light. So, my next challenge will be to actually plant a tree on it. Perhaps, more on this later.