I know how to make a reproduction of a fish head (gills closed) with alginate but how would I make a reproduction of a fish head with open gills or semi open gills. Would I want to put something inside of the fishes head to keep the alginate from getting inside? Thanks
Gerald
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If your going into open gills and you want to show the gills in your fish then forget about using alginate. You will now go into the world of silicones for this. You can use plaster but I'm a sili guy. I would say get some books on this thou it can be expained here but it would take to much time. A quick run down is the parts need to be casted seperately to work out right. you can do it all at once but you will need to put some kind filler inbetween the gills and then after casting you wil have to grind the gills out. It's been tried many times and it's not for the faint hearted.
Sever the gill arch from the dorsal and ventral sides. Array the gills as you would like them to appear. Place the raker side down in moist paper pulp or water-based clay. Cast the gills with the first side application of the alginate. Follow the alginate immediately with a backing shell of plaster about one half inch thick. When the plaster has set, invert the gills, alginate and plaster shell as one unit. DO NOT SEPARATE. Using a squirt bottle, clean the clay or pulp from the raker side. Apply petroleum jelly to the edges of the plaster oon the first side shell. The alginate will not stick to itself, so there is no need to apply a separator to it. After cleaning, apply the alginate to the raker side. Follow the second side alginate with a second thin plaster shell.
When the second side has set, use a scapel and a knife to carve a sprue port at the seam of the two mold halves at the bottom side of the gill raker display. Cast gills. Use a thin solution so that you can "glug" the mold by rocking it back and forth to insure against trapped air. If you desire, the alginate may be cast in plaster to obtain a master to chase and correct prior to making an RTV mold for production. If production is your goal, the gills and the attachment points should be keyed to allow easy assembly of the two components.