Suggestion for a primary school assembly

Show the children a handful of sand, or ask whether they have seen some sand,perhaps on a building site or perhaps at the seaside.
Sand does not cost very much. Would the children expect sand to be a main ingredient, or component, of something very important to us, and something that can be very beautiful?
What do the children think can be made from sand? (They may suggest 'cement' and that is quite right.)
But sand is also one of the main things that make glass. Sand is mixed with other very cheap ingredients, potash and lime, and the mixture is then heated.
We use glass every day: we drink from glasses; we have glass bottles. Our windows are of glass.
This glass is transparent. We can see out from our windows and the sunlight can come in.
But there are some special windows where the glass is coloured so that when the sunlight comes in, we see beautiful, jewel-like colours. We call this stained glass. It is made by adding something called a metallic oxide to the ingredients. For example, if you add copper the glass will be a ruch red. If you add cobalt, it will be blue.
Sometimes people have stained glass in their homes, for example there might be a stained-glass panel on a front door.
But where do we most often see stained glass? In churches and chapels. Why? Perhaps because people wanted their places of worship to be especially beautiful as a way of praising God. Perhaps because stained glass can be used to make pictures in the windows and when we see the rich colours and the beautiful pictures, we think about their meaning.