: So - how does one obtain masses of the proper ratios?

Get a good scale, or use a lot of identically weighted common objects.

For example, there are about 153 pennies to a pound, so a roll of 50 pennies is about 1/3rd of a pound. And two rolls of pennies should be the same weight, but you can determine this simply with your balance beam. If they balance they are the same mass. now get a third roll of pennies and compare it to the first two so that you are certain that all three rolls are identical (or as close as you feel is sufficient)

Now put a cup on the left and the right sides of the balance beam, equally distant from the pivot. This brings it into balance and negates the mass of the cup. Pour into one cup as much resin as you like. If your ratio is 2 parts resin to one of hardener, slide two weights along the other side of the balance beam until the cup comes into balance. Two weights equals two parts of resin. Now, add the third weight at the same location as the first two, and add your hardener until the beam is back in balance.

If your ratio is more like 100:43 by weight, then unwrap your coins and use 100 pennies for your first (resin) pour and add 43 cents more (at the same location) for your hardener pour.

If pennies aren't heavy enough, get a few rolls of nickels, or even quarters. Whent he boat is finished you'll have enough change to treat everyone to soda pop at the launching.

If you use pennies, you may want to check the dates on them. Newer pennies are copper-plated zinc, and older ones are solid copper. There may be a slight difference in weight -- but this is easily checked and compensated for -- jsut get a few more pennies and either use all newer ones, or all old ones.

For heavier weights you can get 1 pound rolls of solder (trim the length to match the weight of several rolls)or you can get 5 pound chunks of plumbers lead at a Home Depot or plumbing supply.

A ziplock plastic bag can be filled with sand or gravel, too. Stick a safety pin through a corner, above the seal, so you can hang it and not have it leak.

hope this helps.

PGJ