Hi Bruce, All.
Plasticene. Gained fame when Aardman Animations used it to make the Wallace and Grommit characters. In the UK its trade name is now 'Newplast'. It comes in a variety of colours in 1kg blocks (which makes it expensive on shipping so I go to an art supply shop) however it does do a lot of SIBs. The block is about 12 x 2 x 1.5 inches in size and is made up from a number of ' round section rods/extrusions which can be peeled off as required. This is useful for mixing colour. eg, I take an inch of blue, and add, say, 1/4 inch of green and 1/8 inch of black. mix well.If this is the colour of the sea you want, that's the ratio to use. Adjust until happy. I only have blue, green, white and black. You do not need a lot of black to darken, its a very intense dye. Does not need baking, the heat of your hands softens it and it stiffens up when not being worked.
Assuming the bottle is going to be on its side, I choose the best side of the bottle, then I mark on the outside of the bottle the level I want, keeping the lower seam level with the top of the sea. This helps hide it and moves the other seam to just the other side of the top of the bottle so that it does not stand out as much.
I PVA a strip of paper with the ship's details, date of bottling, my details, etc on the inside bottom, with the print facing out. Once dry, the plasticene can go in. I use 'sausages' fed through the neck then flattened using whichever tool is best for the job. My new favourite is a length of stainless steel rod that detached from a badly made barbie grill, with one end bent at right angles, the ends having been ground flat and smooth. The glass can play tricks on your eye so have an occasional look through the neck as the plasticene goes in. Once the basic sea is in, then shape the waves, put the hull in, make the recess, add foam etc, and remove the hull. The plasticene never really hardens, just stiffens up, so grips the hull nicely during trial fits, but releases easily enough to get the hull out again. I tend to work with split hulls so the bottom can stay in when finished.
I have started to coat the sea with slightly dilute PVA to give it a gloss shine. It takes a few coats. I also glue the hull in as well.
I have always found holding the SIB in the bottle whilst working on it a bit of a problem. I acquired an Amati SIB kit at our convention (I'll do a build log eventually), and it shows way of holding the SIB in the bottle that I'm going to try. It consts of a 'C' shaped piece of brass on the end of a rod. The 'C' is the shape of half the hull, from bow to stern, with the other half being thread from the far end of the 'C', through a hole at the fwd end and out of the neck, the whole being a type of lasso. It would allow the SIB to be held, manoeuvred, positioned and then released. Excuse bad drawing, but it should get the idea over.
Another method I saw on a video (can't remember which one) was to use a length of dowel between the SIB and the top of the inside of the bottle, basically just jamming it in place. (never tried this)
I've never noticed the plasticene causing any condensation.
I also found this link and I've been trying to work out if the stuff could be used in a bottle.
AK water gel
Have a good Easter break