Outcome

The first step in this process, was to start forming my silicon mold. I started this process by putting white clay around half of my clay umbrella handle from the previous project. Then I built a box without a top around the clay and my handle using foam core. Once this step was complete, I made indents in the white clay and poured silicon into it after removing the air bubbles. 

Once I had one half of my silicon mold, I removed the foam core, white clay, and my original model. I also removed all the white clay from my model. Then I remade a box without a top out of foam core, and poured the other half of my silicon mold around my original model.

Then I sliced my mold in half, to open it back up. I had a hard time finding the parting line between the two molds, which can be seen in the way certain parts of my mold were slightly detached or cut where they weren't supposed to be. However, other than that the silicon turned out alright. I then cut a pour hole into the half of the mold shown in the lower half of the picture above. Also pictured are two small holes that I cut later to get rid of air bubbles at the top of my mold. 

In pouring my second silicon mold, I also found that some resin had seeped in below my clay part. This meant that there would be an indent in all of my castings that I would have to sand out later.

For the next step, I had to put the silicon back together, and then rubber band it before pouring in the resin. As seen in the picture above, when pouring the second half of my silicon, I did not leave enough room in my foam core box to pour the silicon fully over my mold. So when I placed rubber bands over my mold to hold it together, I also placed a piece of plywood over the back to reinforce this area of the mold. When my mold was sealed, I started my first pour of resin into the mold. After the pouring was complete, I placed my mold in the pressure chamber to help get rid of air bubbles as the cast formed.

In one of my earlier molds, you can see that I pushed the funnel in too far, with the extrusion on the right. You can also clearly see the seam line from where the molds meet, and once again, the part of my silicon mold, where some resin seeped in beyond my original clay part.

Some before pictures of the part I decided to sand.

An after picture. The seam line is almost gone, although there are still some air bubbles at the top of the part.

A comparison to another casting I had made. Partway into sanding this one, I had brushed excess resin on the top to try and cover some of the holes left by the air bubbles. This actually worked quite well but I had already spend a good deal of time sanding the other part.

A look at all the castings made in order from left to right. (The leftmost being the first casting). I initially favored the blue coloring, as I thought it would be nice for the umbrella. I actually poured blue dye into my first cast but it was not enough. By the time I got to my third or fourth mold, there was no blue left so I switched colors. I had anticipated the bright pink one (the second to last) to turn out red, and when it did not I put much less dye in for my last casting.