A few months back a kind individual gave me a ciborium veil that his wife had made. I was finally able to put it into use on Holy Thursday. (For various reasons which I won’t get into here, we will not yet be using it on a regular basis.)
On Holy Thursday, it is appropriate for the ciborium to be veiled as it is processed through the church to the altar of repose at the end of Mass. In fact, the ciborium veil used to be required whenever the ciborium contained consecrated hosts. (The veil is not put on until the hosts are consecrated.) The use of the veil was never forbidden, but has certainly fallen out of practice in most places.
I don’t have access to the various liturgical books at present, but I have always understood that the Blessed Sacrament is technically considered to be “exposed” when the ciborium does not have a veil on it.
Here is a photo of the veil over the ciborium in our tabernacle:
The basic reason for veiling the ciborium is because we veil all things that are sacred. Hence it is common for the altar to have various veils over it (at least a linen cloth, but not excluding even other types of cloths that cover it entirely). This is one of the reasons why priests wear special vestments. This is why we often see veils on tabernacles.
It’s also a reason why we should dress modestly — our bodies are sacred!
If you want to read more about the Christian understanding of veiling, there is an entire chapter on it in Martin Mosebach’s book The Heresy of Formlessness, which I notice is available also in Kindle format.
It used to be a real art form to make these veils. Nuns used to paint beautiful Eucharistic designs onto silk, or embroider delicate patterns. There were also some practicalities that developed with time as well. For example, since the veil should be removed before you unlid the ciborium – in case there are any particles on the underside of the lid (so they will not end up on the veil when you put the whole thing down on the altar), and also, in case the ciborium was rather full and the veil should sweep some of the hosts out of it while it was being removed – sometimes veils were made with a little loop sewn onto the top that made it easier to pick up with the finger and lift the veil off. (Modern variations on this old trick have been accomplished by sewing on a small plastic ring.)
Of all the liturgical paraments, ciborium veils would probably be the easiest to make. It would be a great project for someone who sews and wants to do something for the church. You make a circle of fine fabric (silk, damask, etc.), line it with satin or moiré or the like, and there is a hole or slit in the center of it large enough to fit over the cross on top of the ciborium. There are other forms — for example, four flaps that hang down the sides of the ciborium –, and of course there are other possible details, such as fringes and so forth, but in its most basic format it is quite straightforward.
Is the ciborium veil used in your parish?