It was primarily used to serve tea to guests. The cover is used to prevent any dirt or dust from landing on the tea. The cover would had helped to keep the tea warm (to an extent).
The gaiwan can be used to brew tea.
No teapot needed. A simple set up of a gaiwan and a couple of teacups are you need to have a great tea session. Place tea leaves in the gaiwan and add hot water. Hold the gaiwan in one hand, tilt the cover a little bit and pour out the tea into the teacups. You only tilt the cover only enough to pour out the tea while keeping the tea leaves in the gaiwan.
You would need to practice to get your 'brewing with a gaiwan right'. Here are some tips
- filling the gaiwan with hot water to only about 3/4 of the gaiwan. This would not make the gaiwan too hot to handle.
- after filling the gaiwan with water, do not keep keep opening the cover to look at the infusion. The tea would lose heat in a hurry and the tea might not be optimally brewed under such 'cooler' conditions.
Still too hot to handle. Yes, brewing with a gaiwan can caused small accidents. A small slip or unbalance can make the cover to slip off and cause a 'breakage'. Your fingers may be accidentally be scalded while you are pouring out the tea.
There are gaiwan-like variations that you may consider adding to your collection.
A Japanese Shibo is a gaiwan except there are grooves on a section of the cup that makes the pouring out of tea without tilting the cover. This balancing act of holding the cover and cup while pouring out the tea, would be easier in my opinion.
Then we have the flared out gaiwan with a spout. This would keep the fingers 'cooler' and the spout, which has a built in filter would keep tea leaves inside the gaiwan when the tea is dispensed.
Still to hot to handle. Use this one in the last pix. Comes with handle and built in spout. That would resolve any heat or accidental spillage issue.