My husband and I raise cockateils and finches. Cliff is really the expert on cleaning these little eggs. In the past 4 years he has broken maybe 3 dozens out of 3000 finch eggs and to date he has never busted a cockateil egg.
With the T pin he makes a small hole in the larger end of the egg.(fig.4)
Finally he places the empty egg on some white toilet paper. (fig.9) (the cheaper the better for some reason)
I also use these eggs, handpaint them and make earrings out of them, or double end bell caps and make a necklace with them. But I use a hypodermic syringe to suck out the contents of the egg, refill with warm water and diluted household bleach or peroxide, dry them and then fill them with a mix of polyfilla (plaster) and tacky glue, insert a toothpick and stand on end in an egg carton to set for several days. Then when dry you can hold the egg by the toothpick, which has set hard inside, and paint or decorate with ease. You can then stand the toothpick into styro foam to dry the paint etc. once finished nip off the toothpick with nailclippers at the base of the egg.
Another link to empty finch eggs: