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ENAMELLING ON COPPER: A STEP BY STEP PROCESS
Photographs and process outline: The Enamelist Society

A word of caution - if you are doing enamelling for the first time it is suggested you do a short orientation course with a trained enamellist. The Enamelist Society, among others, runs courses for beginners in both Delhi and Mumbai.

In copper enamelling, as in jewellery, a powdered coloured glass called enamel is applied to the copper base. The whole piece is then subjected to high levels of heat and as the glass enamel melts, its thermal expansion matches the expansion of copper, allowing it not only to fuse to the metal, but also to remain firmly attached to it when it cools down again.

MATERIALS REQUIRED

  • An enamelling kiln preferably with a temperature control
  • Copper pieces of 20-22 gauge thickness cut to the required size
  • Plastic trays to hold solution of water and sulphuric acid - all containers should be of plastic as metals react to acids
  • Sulphuric acid
  • Tongs
  • Oven gloves
  • Brush to scrub the copper piece
  • Vim
  • Brushes to paint with
  • Enamel colours
  • Ball clay
  • Sharp well pointed pen or marker
  • Tarragon gum
  • Spray
  • Sieves
  • Colour palette
  • Paper, butter paper, or transparent plastic
  • Scissors
  • Pencil
You will need the following in your work space
  • Sink with a water source
  • A table with a big table top on which you can move your materials easily
NEVER FORGET....
  • Enamelling is done on metals that have a higher melting point than the enamel e.g., copper, gold, silver and steel. Brass and tin have lower melting points than enamel and hence should not be enamelled using this technique.
  • Colours should be washed with water before using them to remove dust and other impurities. This improves the brightness and transparency of the colours.
  • Different colours of enamel have their own specific firing characteristics, and each must be tested to determine how it will fire and look. Over-firing sometimes burns out the colour and sometimes makes it transparent.
  • Lighter colours do not show on darker colours unless they are opaque. However remember that vitreous colours have a higher firing temperature than industrial colours. Therefore applying industrial colours over vitreous colours often cracks the top industrial colour.
  • Too thick a layer of enamel tends to crack and transparency of colours is affected, whereas too thin a layer will burn and become blackened during firing.
  • Some colours do not fuse: for instance blue and yellow together do not yield a green; they stay is as they are.
  • TO SWITCH OFF THE FAN - enamel flies and soon spreads all over the room.

STORAGE OF ENAMELS
Although enamel is manufactured in a chunk form, the type most commonly used is ground so that it resembles fine sand. Many enamellists wash or sift the ground enamel to sort it into the desired grain size.

Colours should be stored in tight containers to protect from dust and oxidation, preferably of glass or plastic.

APPLICATION METHODS
Remember that enamel colours have to be ground finely and graded by sieving through various gauges of sieves, before use. There are two basic ways enamel colours are applied on the metal surfaces.



DUSTING: Dry colours can be dusted through sieves onto the base metal. Usually a gum and water solution is applied on the base so that the dry colours do not blow away. Enamels are available in forms other than just powders. Colour sticks, threads, and little chunks or crystals of colour, for example, are often popular and can sometimes be placed on the base to give a different effect.

WET CHARGING: Wet colours are those that can be mixed with water and a small amount of gum and applied with regular sable brushes. Ceramic oils and glycerine can also be used as a mixer.

FIRING OF ENAMELS
Firing is the most critical part of enamelling. Under-firing gives a grainy appearance to the enamel and the enamel does not get fixed to the metal surface properly. Over-firing often discolours the enamel. Kilns should be preheated to the required temperatures.

DISPOSAL OF MATERIALS
It is important to neutralize the sulphuric acid solution with boric acid before disposing it. The enamel colours should not be disposed off down the drain pipe - as over time they will corrode the pipes. Instead collect the waste, wrap it in paper and then dispose it.


  STEP BY STEP PROCESS
1.

Remove all surface impurities from the copper piece (20-22 gauge thickness) by putting the copper piece into a preheated kiln. Use tongs for handling the piece.

2.

Leave the piece in the kiln for a minute or two so that the impurities are burnt out. This process is called annealing.

3.

Remove the copper piece from the kiln and put into a water bath to cool the piece and remove the burnt ash-residue that you will find on the surface of the piece..

4.

Take out the copper piece from the water, using tongs, and dip it into a solution of sulphuric acid and water made in a ratio of 1:7.

5.

Leave the copper piece for a few minutes in this solution. This helps remove the remaining grease and impurities from the copper piece.

6.

Remove the piece from the sulphuric acid solution, using tongs, and dip into the water bath again, ensuring that the acid solution does not drip anywhere.

A word of caution - remember the acid solution is strong and can burn you.

7.

Scrub the piece well on both sides with a brush. Use vim if necessary. The copper piece should glisten.

8.

Do not handle the piece directly with bare hands - instead hold the piece from the sides - the fingers or thumb should not rest on the surface of the piece, even accidentally, as this leaves residue oil on the copper piece and affects the enamelling.

9.

Wash well in running water removing all traces of the cleaning agent used as well as the surface grease and all other impurities.

10.

The copper piece should glisten.

11.

Next, a ground coat of wet enamel is applied to one side of the copper piece. The enamel solution should be slightly watery and can be dabbed on with a brush.

12.

Cover the full piece properly and allow the enamel to dry completely. Wipe off all extra enamel that may have gone to the other side.

13.

Fire in a preheated kiln for 1-11/2 minutes. Firing the ground coat at 830 degrees celsius envelopes the metal in glass. This process is known as counter enamelling.

14.

If the enamel continues to be grainy it usually means it is under fired and needs to be further fired. If the piece is warped then immediately put it under a weight - it will straighten out. Alternatively drop it on the floor and stamp on it.

15.

Counter enamelling is done so that the tension of the piece is the same on both sides of the metal and will eventually ensure that the metal does not warp or the enamel crack over time. The metal and the enamel expand and contract at different rates when heated, counter enamelling to some extent takes care of this.

16.

Cover the second side with the opaque enamel solution of the colour that you want.

17.

Cover the piece completely.

18.

After ensuring that the entire side is covered with the enamel solution, knock the piece on the side with any hard object like a pencil. This ensures that the enamel solution spreads uniformly.

19.

Allow the enamel to dry. Now you could scratch a design on the dried coloured enamel solution, using a sharp well pointed pen or marker. The line impressions should be deep enough to expose the copper base.

20.

Fire for 1-2 minutes.

21.

The firing burns the exposed copper lines and turns them black, while at the same time melting and fusing the remaining enamel to the base. This is technique is known as sgraphito.

22.

If required excess enamel can be removed using a stone file.

23.

The copper piece can be further worked upon by applying colour in various ways. In this case wet enamel with a paint brush.

24.

Another way is to cut a stencil in an desired pattern and dust the colour over it. To ensure that the colour does not blow away the piece is first sprayed with a solution of tarragon gum and water. The colour then settles on the exposed piece.

25.

The stencil is lifted from the copper piece and the piece fired after drying.


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