Our class makes Trinity punch for the congregation. We use a yellow fruit juice (pineapple is good, or a tropic blend) to represent God the Creator. Think "let there be light" (yellow) or the creation of living things like fruit trees. Grape juice represents Jesus Christ (reminiscent of the wine of the last supper, the wine of the wedding at Cana, the "I am the new vine", etc)And a clear carbonated beverage represents the Holy Spirit (invisible, but effervescent). The Middle English word for spirit was "sprit" or "sprite", so any beverage with a similar sounding name would be especially meaningful.
When the liquids are still separate, they each have their own identifiable character or "personality". When combined in a punch bowl, one can still distinguish their flavours and sense what they contribute to the whole, but they cannot be separated. Just like the Trinity.
I have had an adult say this metaphor helped her "understand the Trinity for the first time". It's a good, clear illustration , and best of all is one that can be shared, another characteristic of the Trinity. i.e. the Trinity is not a "static triumverate" but an active relationship, both internally between the three and externally with all creation.
Larik (Guest) adds:
I also did the Juice example. It worked so well! Then again I asked why it's a good and why it's an imperfect example (imperfect because we say the Father is God, but we don't say that the yellow juice is the punch, it is only a part of the punch). One of my students got the fact that once mixed, the juices are inseparable.
One of my students even knew of the 3 states of matter example, without me even talking about it, how we have liquid, gas, solid, all the same material, but in 3 forms.