Can you put a spoon in water in the microwave?

No. Glass is an insulator and generally microwave safe.

Use a low power setting to avoid burning your milk.

However:

- Glass that has any metal on it or foil labels will cause sparking and should not be used in a microwave.

- Older glass or any crystal that is faceted, or that contains lead will heat up and possibly shatter in the microwave.

- Any regular glass that is heated unevenly too much will crack or shatter.

For example, if you have a glass half full of something quite dense (like gravy), and microwave it for a long time, the lower half of the glass may become much hotter and cause it to shatter.

This is common with glass plates, I can't nuke my inexpensive glass plates for more than 4 minutes without breaking the plate.

If you're unsure about the microwave safety of any glass

1) Use a short amount of time (ie: 30 sec) and watch for any sparking and carefully test the glass to see if it is getting hot.

2) Use a defrost setting which will allow heat to disperse slowly and evenly.

- Finally, any glass that is heated to a great extreme (for hours) will begin to melt, at which point the glass becomes an ionic conductor, and will absorb microwaves and continue melting further, releasing small amounts of super-heated flammable gas that will burn.