Numbers 4:13

And they are to take away the burned waste from the altar, and put a purple cloth on it;

Exodus 27:1-8

And make an altar of hard wood, a square altar, five cubits long, five cubits wide and three cubits high.

Exodus 39:1

And from the needlework of blue and purple and red they made the robes used for the work of the holy place, and the holy robes for Aaron, as the Lord had given orders to Moses.

Exodus 39:41

The robes for use in the holy place, and the holy robes for Aaron and his sons when acting as priests.

Leviticus 6:12-13

The fire on the altar is to be kept burning; it is never to go out; every morning the priest is to put wood on it, placing the burned offering in order on it, and there the fat of the peace-offering is to be burned.

Numbers 4:6-9

And putting over it the leather cover and over that a blue cloth; and putting its rods in place.

Numbers 4:11-12

On the gold altar they are to put a blue cloth, covering it with a leather cover; and they are to put its rods in their places.

Treasury of Scripture Knowledge

Summary

And they shall take away the ashes from the altar, and spread a purple cloth thereon:

The embers of the sacred fire seem to have been removed in the grate, which was carried apart from the brazen altar; both being covered from view by purple cloths

General references

Bible References

The embers of the sacred fire seem to have been removed in the grate, which was carried apart from the brazen altar; both being covered from view by purple cloths

Numbers 4:6
And putting over it the leather cover and over that a blue cloth; and putting its rods in place.
Exodus 27:3
And make all its vessels, the baskets for taking away the dust of the fire, the spades and basins and meat-hooks and fire-trays, of brass.
Exodus 39:1
And from the needlework of blue and purple and red they made the robes used for the work of the holy place, and the holy robes for Aaron, as the Lord had given orders to Moses.
Leviticus 6:12
The fire on the altar is to be kept burning; it is never to go out; every morning the priest is to put wood on it, placing the burned offering in order on it, and there the fat of the peace-offering is to be burned.

General references

Numbers 4:8
And over them they are to put a red cloth, covering it with a leather cover, and putting its rods in their places.

Basic English, produced by Mr C. K. Ogden of the Orthological Institute - public domain