A Curtain is a calcite formation in the form of a wavy or folded sheet hanging from the roof or wall of a cave.
A curtain forms when water runs down the roof or the wall of the cave. If the ceiling is nearly horizontal, the water will form a stalactite, if the wall is nearly vertical, the water will form a sinter galery.
But if the angle is in between - about 45° - the water will not fall down, but run down the wall. It will always use the same path.
While the water runs down the wall it looses carbondioxide (CO2) to the atmosphere of the cave and as a result deposits calcite in a thin vertical line on the wall. This line grows and grows, at very soon there is a small rim.
Once there is this small rim the water has no possibilty to leave this path. It always follws this path like a train follows its tracks.
Curtains are normally translucent and resonant. Both characteristcs depend on the thickness (or thinness) of the curtain.
As the curtain growth from a very thin line - as thin as a drop running down the wall - it normally is very thin. And as it consitsts of small calcite crystals, it is translucent.
As climate on the surface changes the amount of water in the cave does. So there are short periods like the seasons and much longer periods like changing sun spot activity.
All changes in the amount of water change the relation calcite/iron oxide and therefore the colour of the depositing calcite crystals. An as the curtain grows in layers, there are stripes inside the curtain. Normally you can follow them fron the beginning to the end of th curtain.
This charcteristic of curtains lead to names like bacon or bacon rind for this formations.