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My method of molding a fish head

Discussion in 'Tutorials' started by scanman, Feb 23, 2010.

  1. scanman

    scanman New Member

    There are many ways to mold a fish head, so I thought I’d share mine. I use this method because I like the detail that using silicone gives and allows me to use small amounts of silicone to cut down on expense. I also love how this method allows for great mouth detail which allows me to bypass using a mouth plug which I am not that comfortable using. The down side to this method is you get one shot to use the mold, so your first pull has to be a good one. I’ll also add this method is not for production casting, but can be used to cast your prototype.

    Materials: Quick curing tin-cured silicone, Bondo, and urethane plastic, mixing cups and sticks.

    The use of a quick curing tin-cured silicone; has two purposes one it is quick curing, the one used here cures in 75 minutes. Second being tin-cured it is less expensive and it is more forgiving than platinum-cured silicones which may not cure if the fish is not completely dry. The fish being used here is a 20” hen brook trout. This method can be used with a closed mouth or with an open mouth/ closed operculum, this method will not well with the flaming bass looking (open mouth/open operculum) that requires a more advanced method.

    Step one- is to wash the fish off in cold water to clean off any slime. Don’t forget to clean in the mouth and under the operculum cleaning the slime off of the gills, rakers and gullet. Then dry the fish including the inside of the mouth, gills, etc. Dry as good as you can.

    Step two- is to position the fish in an upright position, making sure the operculum are free. Mix up a small amount (30cc) of silicone and pour in the fish’s mouth coating everything. Some of your silicone will run out below the operculum which is O.K. for now. This coat is used to mold the mouth and seal the mouth so your next pours of silicone won’t run out under the operculum. Let cure. After curing slightly lift up the operculum and trim off any silicone that has run out, other wise it will stick the future pours encasing the head.


    Step three- mix up another batch of silicone (60cc) and pour in the mouth and then over the head of the fish coving all the head. Let cure.


    Step 4- Cut up some extra cured silicone into small chips and drop it in the mouth to fill up the mouth, then mix up another batch of silicone (60cc) and pour in the mouth and over the head. The fresh silicone will combine with the chips and become one, making the mouth mold sturdy. Let cure.


    Step 5- Mix up one more small batch of silicone (30cc) and pour over everything. Let cure. Approximately 5 hours has passed from start to this point.

    Step 6-After silicone is cured apply a thin coat of straight Bondo about 3/16” thick or thicker if you want. This will act as the “Mother Mold”. After the Bondo is cured than you can carefully demold the fish.


    This picture shows the inside of the mold.


    Step 7- now is the time to clean up the mold, trimming away any severe undercuts. Also now is the time to trim off the gills, leaving just the impression of the gill arches. If you don’t do this it will be impossible to remove the silicone after it is casted. Picture of the mold all cleaned up.


    Step 8- is to cast the fish head, no mold release is needed. You can fill the mold with urethane plastic and make a solid cast, which you will dremel out later to your specification. The other way to cast is put some urethane plastic in the mold and rotate it around covering all parts of the mold. This produces a thin shelled mold, usually requiring at least two applications of urethane to make sure the walls are thick enough. Here are some pictures of the finished head, notice some of pits from where the customer had vacuum-packed the fish. These will easily be smooth over with epoxy. Remember the cast will never be better than what is molded. Total cost in supplies is around $11.00


    Here is a carp done with this method

  2. Hi Jeff. I really like your method, but what is the quick curing tin cured silcone you use? Can you give me a brand name or tell me where you get it? Great tutorial! Thanks!!!! George

  3. scanman

    scanman New Member

    I wasn't going to push a certain product line, but more the type of silicone. With that being understood the products used here are from Smooth-on, the silicone is OOMOO-25 and the urethane is SmoothCast-300
  4. CarlScroggins

    CarlScroggins Oct. 25 1985...It was a good day.

    Is there any damage to the fish? Can you make this mold and still skin mount that fish? I have been tempted to make a silicone mold of a customer's fish before, but always scared of damaging the fish. I am pretty positive that a bondo/fiberglass mold would destroy a fish for a skin mount.
  5. scanman

    scanman New Member

    Generally not, if you take your time demolding the fish. If any damage it would be from pulling a scale. Since the silicone separates the fish from the Bondo and since very little Bondo is used there is no heat damage. This particular fish will be a skin mount using the cast head.
  6. boarhunter67

    boarhunter67 Well-Known Member

    I'm just a little confused on how you get the replica out of the mold. Is the silicone pliable enough to allow the gills to slide out? I have made molds with regular silicone before and usually make the replica by pouring fiberglass resin in. Am I using the wrong silicone or is it the resin that is hindering me. I usually do just the outside of the fish and leave the mouth alone, but I never like that I don't like that my mouths don't have much detail.
  7. scanman

    scanman New Member

    I'm just a little confused on how you get the replica out of the mold. Is the silicone pliable enough to allow the gills to slide out?
    Actually the gills are trimmed off the mold leaving just the impression of the gill arches. If you look down the mouth of a fish when the operculum are closed you don't see the gills but the gill arches. You can see in the pictures above where the gills have been trimmed off. As far as demolding, it is as I stated above, this is a one time use mold. The silicone in the mouth of the mold is actually removed in pieces. This is because when you look in the mouth of a fish it actually fans out in back, depending on the species off fish. Now a mold that is made to produce many pieces, the mouth mold area in back is made straight or tapered inward to allow for easy demolding.
  8. boarhunter67

    boarhunter67 Well-Known Member

    That makes more sense. Can you show a picture of the mold separated into pieces? Do you pin them together before pouring, then remove the pins and pieces?
  9. scanman

    scanman New Member

    I think you miss understand, this is a one time use mold for casting a fish head that you want full mouth detail (tongue, gill archs, gullet) or to cast a prototype for a production mold. When I say that it is cut to pieces to demold the cast I mean the mold is destroyed. The only way around not destroying it is to alter the mold before casting. Like making cuts like in the picture below. I designed the method to use as little silicone as possible as compared to the cup method. With this fish I only used about 6 oz of silicone.
  10. boarhunter67

    boarhunter67 Well-Known Member

    Thanks for clearing that up. I looked at the "cup method" a couple of times, but had the same question about it.
  11. GBRUCH

    GBRUCH "I am nothing without christ".....John 15:5

    Why do you need to destroy the mold Jeff. It looks like what I do except your RTV is thinner and you jacket it.

    I think you could simple pull the mouth plug out in one piece since it is trimmed back.
  12. scanman

    scanman New Member

    Hi Gary, I have had some success with warmwater fish pulling the mouth plug, but with coldwater fish not so much success especially with fish where the mouth is more closed then the one pictured. The mouth plug being wider because of the arch and floor of the mouth. The mold usually rips at the mouth line first and then the mouth plug. I know this is because of the type of silicone I am using which is a tin-cured silicone which has a tear strength of about 40 pli. which is pretty low. But I choose that type of silicone because more often than not when I have tried this technique with a platinum-cured silicone I end up with areas on the mold that will not cure. Now if I have a head that is worth reproducing, I will make a mold of the first cast using platinum-cured silicone which I have no problem demolding. Nice hearing from you and I still want to take that carving class if I can financially get back on my feet.
  13. cthayne

    cthayne New Member

    Exactly what I was looking for.
  14. glassmonkey

    glassmonkey New Member

    I am wanting to learn to build better mouth plugs for my reproduction fiberglass fish do you know if this will work for just the mouth insides, as my molds have the heads in them Thanks
  15. Rob43

    Rob43 Member

    That's awesome