Scyphocrinites elegans - mold.
As I mentioned in the making of our Placenticeras meeki mold, my presses present size constraints that are very precise and inflexible. My small presses have size constraints of 18 x 24 inches and 6 inches deep. My large press beds are 24 x 36 inches and 3 inches deep. In addition to the size of the press I must take into consideration the frame for the mold which is usually an inch and a half wide. Also you must allow for 1/2 inch space from the fossil to the frame. You need to also allow for 1/2 to 3/4 of an inch for each board on both top and bottom of the frame to contain the expanding cast material. Additionally you must allow for 1/4 inch above the highest point on the fossil to make certain that the mold will not be weak at any point and tear or become damaged during usage.
So, given the press and frame constraints (which must be contained within the press beds to prevent the expansive resin from expanding beyond the mold) the actual fossils or specimens you are able to reproduce are somewhat smaller than the dimensions of the presses. The maximum size of the fossil or specimen for the small press is 14 x 20 x 5 inches. The maximum size for the large press beds is 20 x 32 x 2 inches. With the large press I also need to allow a little extra room on the length to ease the insertion and extraction of the mold from the press bed.
This particular fossil presented problems which seemed that it might be impossible to create a cast. The dimensions of the original specimen are 26-1/2 x 25 x3-1/2 inches. With a frame for the mold the length would be 30-1/2 inches long and 29 inches wide. These dimensions are clearly outside anything that I am able to work with. With regard to the depth some of that may be eliminated by droping the specimen in a hole when the mold is made. Another issue with this specimen was that there is a low point (that doughnut on the left side) that needed to be taken into account so that there wouldn't be a hole in the middle of the cast. You can see from the photos in the third row that you must consider the full depth of the mold, the height of the highest point on the fossil and the quarter inch clearance. The last item is the depth of the lowest point on the fossil. This would not be a problem if the fossil (or item to be molded is less than your bed depth. If on the other hand you must reduce the thickness of your specimen by dropping it into a hole, then you must check the lowest point to insure that you don't wind up with a hole at some point because it was outside of the mold tolerances. Since this specimen was so thick, there was no way to reduce the entire amount of detail to just under two inches (the specimen was about 2-1/2 inches thick). We allowed for the mold to extend into the base plate by creating a window which included the higest points of the specimen plus 1/4 inch above the highest point on the specimen.(middle picture of fourth row). These are the toughest problems to overcome with a large item to be molded. There is one other which will be discussed at the end of this discourse.
As with all fossil specimens, there is some pre-molding preparation that is necessary. This specimen was no exception. The original is a rare and wonderful full Scyphocrinites elegans crinoid specimen. Any cracks or opeings must be filled with clay (first two photos) to prevent the silicone molding material from seeping in and causing problems when the mold is removed. The problems being either pulling the fossil apart or filling the cracks in the fossil with blue silicone (not very attractive or of much scientific value). Additionally with this particular specimen there is a small window under the head and neck of the crinoid. To allow for the cast to also have this window, a thin wall must be created (photo #3) to allow the mold to slide off the specimen and subsequently from the cast. This wall which will come out on the cast is then cleaned away to create a window on the cast. Also some specimens, this one was no exception, need a little repair to make the cast as complete and perfect as possible. The highest point on the head was missing a small portion (pink clay, first photo row 3 and photo 3, row 1)
Once the fossil is ready for casting (all cracks filled and imperfections addressed), a clay base is created to fill the gap between the specimen and the top of the hole the specimen was dropped into (picture 3 row 4). A frame must then be created to contain the mold. The frame should be 1/2 inch from the specimen at its closest point. You will need as many sides as makes sense, In this case nine sides were needed so an excees of molding materal was not needed. Using only as much molding material as necessary is a critical consideration since we have paid up to $1,600.00 for 5 gallons of silicone. There are less expensive silicones available for making molds, but it doesn't hold up as well as ours so in the long run after remaking the molds multiple times it ends up costing you more going on the cheap than paying the piper up front. The silicone we use is the most expensive, but our molds give us a longer lasting mold and truer casts. This particular specimen used about 3/4's of a bucket.
This specimen was quite heavy and required moving occasionally. Each time it was moved created the possibility of a hairline separation between the clay and specimen and frame base. This had to be constantly checked (pictures 2 & 3 row 6). If a hairline separation is not caught then the silicone will leak through and possibly be all over the place (ruining the possibility of being able to make the mold at all, in some cases). So, this is a very critical step. Next up, the frame must also be sealed with clay to prevent silicone from seeping through (row seven). Since this mold incorporated the base plate as part of the mold frame, an additional bead of clay was needed between the frame and base plate to seal that area (photo 2, row 7). Before the base plate is attached to the frame all surfaces (except the specimen, which will be sprayed with a mold release) must be covered with petroleum jelly to prevent the mold from sticking to them. The petroleum jelly will also help fill any potential hairline separations (but, don't count on it).
Once the specimen is ready for molding and the future mold base is attached, it is time to pour the mold (row 9, picture 1). Picture 2, row 9 is the completely poured mold. A critical factor here is that the silicone must be allowed to flow to all points on the specimen with no bubbles and that it be absolutely level. Another point to keep in mind is that the top of the mold must extend a little way above the top of the frame. This allows for the top side of the pressure bed to form a tight seal on the mold and frame and keep the resin for the cast from escaping and creating a huge mess (row 9, photo 3). The paint stick in the picture is 1/8 inch thick. When the stick is removed it will allow the mold to rise above the top of the frame creating a good seal for the cast.
Once the mold is poured it must be allowed to cure. Usually one to two days is sufficient. Thicker molds may require a little more time. It is always wise to err on the side of caution and allow for a little longer cure time. If you pull the mold off too early and the silicone has not fully cured, there is no way to put it back on. You must start all over, It can get quite expensive, especially with a specimen the size of this one.
The first picture in row ten shows the mold base with the cut out removed. This base allows for the specimen to be about 3/4 of an inch deeper than would have other wise been allowed. The second picture shows the frame with the 1/8 inch paint sticks removed from around the mold. At this point the paint sticks are no longer necessary and they are removed from the frame. You will also notice in the pictures in row 10 that there is a couple areas where the silicone did not fill in. It is possible that it just didn't flow to those areas or that air got trapped there and couldn't get out. If these areas create a problem for the cast, they can be filled in with cardboard and tapped to hold it in place. So, all is not necessarily lost. Those types of problems are much more serious on the other side of the mold where the specimen datail is found.
You can see the inside of the mold in the photo number one of row eleven. Having addressed the thickness issue of the specimen by using a cut out in the base support for the mold, the last hurdle that I had to overcome with this specimen was the width. As I mentioned earlier the widest a specimen can be, and still fit in the press is 20 inches. That allows for the frame on both sides (three inches) and 1/2 inch on either side between the specimen and the frame (one inch) to still fit in the pressure bed. This particular specimen is 25 inches to begin with and could not be reduced in any way without damaging the specimen. So, we made the mold and hoped to figure out a way to manage the making of the cast with five to six inches hanging out of the press. We hoped that by placing a couple of large wooden clamps on the portion hanging out of the press that it would allow us to create this exceptional crinoid cast. Fortunately it did work.
The down side of using the clamps is that time is not on our side. The two part resin must be stirred for ten seconds. The stirring instrument must be rinsed off in laquer thinner (another second). The resin must be poured from the bucket into the mold (three seconds). Then the mold must be tipped from side to side and top to bottom to insure that the resin is in contact with all surfaces of the mold (another 8 - 10 seconds). We are now at about 24 seconds. Now you need to place a sheet of mold release paper over the top of the fresh resin, place a board on top of that and get the mold into the press (another three seconds). The clamps must now be placed one on either side of the extended mold to insure a tight hold on the upper and lower edge to prevent the resin from expanding out of the frame (two to three seconds per clamp). The whole process can take no longer than 30 seconds. If it takes longer you can see the result in the third photo in row eleven. That was a couple of seconds late. If you don't get the mold in the press and the clamps on, the mess will be even greater. An additional issue is that when the temperature is higher the time to process is shorter. Casting temperatures range from 70 to 80 degreees. At the lower end you have a couple of seconds more time and at the higher end you have a few seconds less time. Without the mold release paper the cast would be permanently stuck to the board placed over the top of the open mold or the press if neither the paper or board was placed on top. Every step is critical.
You can see a completed cast in front of the mold in row twelve and well as a painted piece next to it. The coloration of the original specimen is a little darker than the painted cast. Some of this is due to lighting. The original specimen also absorbed some of the oil from the mold release (making it darker) and also had some darker coloration due to materials used for the repair of the original specimen.
To see some of the other steps in the mold creation process, please view other pages in this web site. Also enjoy the other products and information on this web site. New additions, and updates, are made to the site monthly.
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Clay fill of cracks in original specimen.
Measuring thickness of original specimen.
Measuring highest point on original specimen..
Insuring that there is 1/4 inch clearance.
Frame must allow 1/2 inch gap to specimen..
This wall keeps the cast edge from distorting in press.
Seams along specimen and frame must be filled.
Vasaline will be used as a final seal and release.
Windowed base is tightly screwed down.
Mold cured and windowed base removed.
Finished mold in frame.
Mold with completed cast.
Clay fill of cracks in original specimen.
Reducing thickness of original to fit press.
Determining lowest point within original specimen.
Window in base allows for a deeper mold..
Gap may be more or slightly less than 1/2 inch.
Once frame is attached, check all seams.
Any gaps around the specimen or frame will lead. . .
A clay bead will be used to seal the base with window. .
Mold is leveled and poured to top edge of base.
Frame removed from mold.
Mold in press with wooden clamps.
Clay repair and thin wall for gap in original specimen.
Clay fill around original to be even with frame base.
Making sure that mold will fit in press.
Before frame is attached, check clay seals.
The gap allows for a thick silicone wall on mold.
Seams must be tight to prevent silicone from leaking.
. . to leaking of silicone and possible mold failure..
All wood and clay must receive a thin layer of vasaline.
1/8" thick paint sticks used to insure gap at mold top.
Notice areas where silicone failed fo flow to.
A couple seconds late getting mold in press.