Cal, the only one I used any tape on was the three tone thing with a long sharp pointed right straight above the conch shell you ask about..I put the tape over the yellow for I was changing the color I had already but on the large portion and wanted a different color. I don't practice enough with the air brush and especially when using the cheap Michaels or HL water base paints is cheap enough to do much more practice also you can crank in the spray fan and draw a line. But the smaller lines will show flaws easier..
Using a set of french curves I traced curved lines on to some clear plastic about 1/16" thick so I could bend it over the rounded things and get better lines that didn't show my shaky puddin and then only spray on every other lines so it would look two toned where the natural wood was one of the colors.. Blow up the picture and you can tell I two toned a few more but still learning for having the air brush in one hand and the piece to be sprayed in the other hand adds to the un even coverage.
Sanding the pieces, the 1x42" disk-belt sander does about 75% of all the shaping of the pieces...I use two machines, one with a 60 grit and the other with an 80 grit belt. Belts can be changed very quickly if I only used one sander. I do use an oscillating drum sander quite a bit but not as often as the 1/42's. My finish sanding is done with a regular electric sander upside down on top of the table saw sittin on a thick rubber pad. One hand to hole the sander and the other hand to hold the pieces....180 or 150 grit only.
Its easier to sand wood that is cupped out so most of what is in this picture is made that way. Sanding cupped in pieces takes maybe 10 times longer to smooth, thats the reason you don't see so many of them.
Only the two groups of coral was brush painted and I did want them wilder in color.
Cal the silver gray cupped in critter next to the one you referenced I probably spent ten times longer to end up as smooth...
Some of the smaller pieces I used a bit that is 1/8" round and made lots of the grooves and was smooth enough I didn't have to do any hand sanding....Its the longer small grooves that a persons hand has to be reshifted to continue that groove is where the quality of a good straight line goes haywire...This is the reason those 2 biggest shells has only drawn lines with the pencil and there I did use a piece of curved plastic for them.
Go back to where I show the first picture with all the pieces finished but with no color added and a few pieces I changed the shapes completely before I added the colors. The big thing down in the bottom left was completely flat on the bottom side.
Man I really love this Steve!!!! I want one! Could be used as a range box too, really cool and hearty. This will last a generation or two, this is one of my favorites you have done, clap clap clap clap!