Okay, I'm not sure what I missed but I sure missed something. I cast a large fish head & fins by making alginate molds then filling with thinned bondo. This was my first molding & casting attempt. The head turned out okay, a few holes/bubbles that could easily be filled, but not bad. It's the fins that I'm confused about. One side of each fin has detail, the opposite side is flat. Also, they are thick; not much (if any), taper from the fin base to the edge.
What the heck did I miss here? Do I need to now mold & cast for the other side? If so, how to make them thin enough? That is, how to get the extra bondo off the back of the fin? Obvioulsy, I missed a step here but I'm not sure of the remedy. Any advice would be appreciated.
Return to Beginners Category Menu
although i haven't treied casting fins yet or even a fish head, there is a great article on casting fins by gary bruch in the latest Breakthrough or Taxidermy Today Magazine. his fins he molds in bondo on both sides and then casts with porakast. good luck.
First off, when casting fins they are pressed together either with the casting material in it or clamped and then poured in. The way your doing it gives you that flat side. You need to make a two piece mold with some keys made into it so when there pressed together they'll line up right and give you the casting you want.
As for the casting material it's not pour a cast at all. It's a product from smooth-on.com and it's called Smooth cast 325.
Aslo it's just not bondo to make the mold of the fins. It's made from resin and bondo mixed together. The mixture sould be thin enough, lets say like maple syurp. This is the first coat, which gets the detail. The second coat it then regular bondo. After the mold are made you need a release agent which is, one part vasiline and two parts minerial spirts. This is coated on both sides,left over night and then one coat the next morning. You can then make a cast of your fins using many different casting materials.
Pretty soon there will be a new epoxy on the market for fin making that will be a nice butter mix that will make an extremely great fins. Plus cost effective!
Bryan , you really dont need a two part mold for fins as you dont see the back side . You only need a very small amount of bondo gel coat on the fins . You can even thin it out a little more then what you use on the head , then just one thin layer of mat . If the back side is too thick , just sand it . You can use a file also . Rick
Thanks for all the help guys. I was trying to follow the method in this spring's issue of Breakthrough. He uses alginate then fills w/ thinned bondo - which I did. I guess it wasn't clear to me that I needed to cast both sides of the fins. If I'm reading it right, according to that article, only thinned bondo is used as fin material.
I guess for now I could just sand or file the back side of the fins until they are thin enough.
Thanks again
Try this, roll out a large part of non-hardening clay with a rolling pin, press the show side of the fin into the clay until it is completely below the clay level, remove the fin, mix up some catalyzed art water or fiberglass resign (you can tint to make nice transparent fins) and pour it in the indention. You now have an economical fast way to make commercial grade replacement fins.
DaveT
I like that! Think I might try that one in the future.