Venetian curtains are thin aluminum or wood slats (chipboard), which can be collected in a very small hole (depends on the height) and that once opened, can be turned on their axis to adjust the light that is going to enter without having to discover the hole.
There are 3 different widths of slats in the case of aluminum ones; 16, 25 & 50mm.
In the case of wooden ones, the width is standard and is 50mm.
Cleaning is through a duster, preferably with the slats lowered and closed.
You can see some models in the link below.
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