COLOURS OF BRICKS

The colours of bricks as obtained in its natural course of manufacture depend on the following factors

• Degree of dryness achieved before burning 
• Natural colour of clay and its chemical composition
• Nature of sand used in moulding operation
• Quality of fuel used in burning operation
• Quantity of air admitted to the kiln during burning 
• Temperature at which bricks are brunt 

COLOURS OF BRICKS

No.	Colour	Constituents Present in Clay
1	Black	Manganese and large proportion of iron
2	Bluish Green	Alkalies
3	Bright red, dark blue or purple	Large amount of iron oxide
4	Brown	Lime in excess
5	Cream	Iron and little lime
6	Red	Iron in excess
7	White	Pure clay
8	Yellow	Iron and magnesia

The artificial colouring of bricks is achieved by adopting one of the following two methods

1. Addition of colouring material
2. Dipping in colouring liquid

1. Addition of Colouring Material: 

In this method the required colouring material is added in brick earth. The bricks prepared from such earth will present the desired colour. The usual colouring materials are iron oxides, manganese, French ultramarine, Indian red etc. This method is adopted when the colouring material is cheap and when it is available in plenty.

2. Dipping in Colouring Liquid: 

In this method an earthenware box which is slightly larger each way than a common bricks is taken. It is filled nearly to 1/2 depth with liquid which is in the form of thick paste. The bricks to be coloured are placed on an iron plate and with a fire underneath they are heated to such an extent that they can be easily handled. One brick is taken at a time and it is allowed to stay for few seconds in the box. It is then placed aside to dry.

The colouring liquid is formed by the addition of colouring material to a mixture of lineseed oil, litharge and turpentine. The proportion of various component of colouring liquid for different colours.

COLOURING LIQUID

Component	Name of the Colour
	Black	Blue	Dark red	Grey
Lineseed oil	1.20 N	570 c.c.	850 c.c.	0.60 N
Lintharge	0.60 N	0.15 N	1.15 N	0.30 N
Turpentine	1.80 N	570 c.c.	850 c.c.	1.20 N
Manganese	1.80 N	-	-	0.30 N
French ultramarine	-	4.50 N	-	-
Indian red	-	-	0.15 N	-
White lead	-	-	-	0.90 N

Following are the advantage of this method-

1. The bricks which are coloured by this method do not lose their colours, when exposed to the atmosphere.
2. It can be adopted for expensive colours
3. It is possible to develop a variety of colours cheaply and easily
4. The penetration of colouring liquid in ordinary bricks ia adbout 3 mm or so.
5. This method can be used for brick wall which are already constructed. The wall surface is carefully cleaned. The colouring liquid is slightly heated and it is applied on the wall surface with a brush.