I use hide glue when making up the blanks for the moulding planes, but I don’t like how the colour of hide glue at the join shows that it’s laminated. So I made a trial run with fish glue as I know it will dry to a clear finish and is just as strong as hide glue.
Animal products is not a gap filler, but hide glue to a small degree will fill some small gaps. Fish glue on the other hand shows no mercy. If the join isn’t tight enough, it will not fill it and will remind you how much you suck at woodworking. This means your work has to be God like and how is that possible?
As you can see in this scrap of beech, I ripped it into four separate pieces, jointed and edge glued each one individually. You can clearly see that the glue did not fill the gap in the top right corner, but the left side was well done so it’s a seamless join.
I haven’t had the balls to try this when laminating the blanks, because I’m sure there would be gaps on such a large surface.
I think in making up the blanks if you don’t want to see a dark brown colour at the join, then white PVA glue would be a better option.