PREPARATION

In general, the electrolyte solutions, all the cathode plates, plate contacts, grids, etc. must be of the same metal as the plates with which you are working, so in the section below I will use the word 'metal' to avoid repetition and confusion. So for example if you are working with copper plates, you will use copper sulphate, and the cathode plate or grid will be of copper, and any other metal like solder, bolts or pop rivets must be varnished. Similarly, if you are using zinc, substitute the word 'zinc' for 'metal'. Never mix metals or galv-etch one metal in the sulphate of another (see the section on ''chemistry of Bordeaux etch' for an explanation)

mixing the solutions

Add the sulphate crystals to distilled or demineralised water until you have a saturated solution - when no more will dissolve. Approximately 500 grammes of copper sulphate or 1 kilo of zinc sulphate will dissolve in 2 litres of water, or 800 grammes of ammonium ferrous sulphate in 3.8 litres. The stronger the solution, the faster will be the rate of etch, but also the electrical resistance will be lower, so if you are galv-etching a large plate and find that your power supply is being overloaded, then you can dilute the electrolyte further to increase its resistance, but will have to increase the time proportionately. (see times and tests). If you then add 3 litres of water to the concentrated solution you will have a 1:4 solution. In the case of a 1:4 copper sulphate solution that means adding 62.5 grammes of copper sulphate to every litre of water.

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plate contacts

The simplest way of making a contact for a plate to be etched, is to tape one or two thin flat metal strips to the back of the plate to be etched. Cut a piece of self-adhesive plastic sheet the size of the plate and put the flat strip against the back of the plate and then stick the plastic sheet over it. This way the back of the plate can be protected against being slightly etched. The flat strip can be bent up to sit clear of the electrolyte and the crocodile clip fixed to it. The strip also helps to lift the plate out of the solution and carry it around.

Left - self adhesive tranparent plastic sheet laid over back of plate to fix copper contact strips.

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left - strip bent up to project out of electrolyte

 

Another method for making a contact with a plate to be galv-etched in a flat deep tray is to solder or tape a flat strip to a small flat plate to lie on the bottom of the tray, which makes a contact with a bare area in the middle of the back of the plate. I will call this a backplate contact from now on. The back of the backplate contact and its strap should be varnished or covered with plastic.

Copper backplate contact with copper strip bent up to project out of electrolyte - strip protected by strong varnish.

 

The back of the plate you are galv-etching need not be varnished, as the electrolytic etching action is strongest on the face directly opposite the cathode. Only the edges and perhaps a strip around the edges need to be protected. If you use plates with backs ready protected, in a flat tray, then you will have to use a cradle to make contact with the bare edges of the plate as described later.

An alternative way of making a contact is to tape a thin flat metal strip to the back of the plate to be etched. Cut a piece of self-adhesive plastic sheet the size of the plate and put the flat strip against the back of the plate and then stick the plastic sheet over it. This way the back of the plate can be protected against being slightly etched. The flat strip can be bent up to sit clear of the electrolyte and the crocodile clip fixed to it. The strip also helps to lift the plate out of the solution and carry it around.
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cathode grid

The method that I recommend for a flat deep tray is to use a grid for the cathode (-ve), made from wires or strips of metal soldered or mechanically fixed to a frame. The frame of the grid should be bent so that the wires of the grid are just immersed in the surface of the electrolyte. The spacing of the wires should be less than the distance from the grid to the plate. A stainless steel off-the-shelf grid can be used for galv-etching, as it will be soon plated with the metal (see later in plating). If you will use the equipment for plating or galvanoplasty (creating a new negative plate against a mould), and will be removing a significant amount of metal from the grid (anode in that case), then you will need a plate suspended to touch the electrolyte. I normally use the standard grid with a plate the right size fixed below it with large varnished clips or fixed with self-adhesive plasic tape.

A simple way of making a grid is to drill a series of holes in two stout strips of metal forming the sides of the grid. The holes should be the size of the metal wire which will form the grid. They can be inserted through the holes and bent to stay in place.

If you use any metal other than the one that is compatible with the plate to be etched it should be varnished to protect it . This applies to any bolts, rivets, clips or hooks to support the grid.
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Copper cathode grid in plastic etching tray 48 x 36 cm. 6 cm. deep,


galv-etching line or tint in a flat tray

To start with, if you are galv-etching plates that have been grounded and needled, or fractinted, you can use a conventional flat etching tray. The tray needs to be quite deep, at least 5 - 6 cms, for the method that I recommend. If you have not got a tray deep enough, you can use the kind of plastic food storage trays sold in supermarkets, because the galv-etch electrolyte solutions are not corrosive, and don't need the special materials required for acids. Don't use metal trays though, even if enameled, in case of electrical short circuits.
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vertical tank

The alternative to a deep tray is a tank in which plates can be hung vertically from a bar or over the edge of the tank.. Vertical tanks are increasingly used for etching and most of them can be adapted for galv-etch if they have sufficient depth to hang the plate and the cathode opposite and parallel with about 5 cm between them. Vertical tanks can be made for galv-etching from large polypropylene or other plastic 'jerry cans' or water storage containers with built -in taps as shown below. It is a good idea to have a tank with a tap a few centimeters above the bottom, in order occasionally to empty it without stirring up the deposit that eventually accumulates on the bottom. Using a vertical tank with sufficient depth is a much better way of doing galvanoplasty or plating, but can be used for all purposes if it will take your largest plate.
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Vertical tank with tap, 35 x 35 x 15 cm holding 18 litres, with cradle and anode copper sheet for plating, made from a heavy duty plastic storage can with the top cut off and edges bent in. The large volume of electrolyte is not exhausted by galv-etching or plating, and does not pose a disposal problem.


supporting a plate in a vertical tank

If you wish to use a larger tank with the plate vertical, one way to suspend a plate and to provide a contact and protect the back is to cut a sheet of self-adhesive plastic sheet to the size of the plate and fix two thin strips of metal against the back of the plate. The strips can be bent over to hang over the edge of a vertical sided tank or to hang from a metal bar across the tank. Contact from the power supply can be made to the metal strips or to the end of the metal bar. If you are using plates with backs ready protected the plate can be held on a metal cradle hooked over the edge of the tank, made from a broad strip of the correct metal with the edge turned up on which to rest the plate with a bare area to make contact with an unvarnished area on the edge or back of the plate.. All the metal bars, straps, clips, rivets etc. must be well varnished against being etched, just leaving the points of electrical contact with the plate bare.

For the vertical tank make a cathode plate of the correct metal by soldering or taping thin metal straps to each end, to hang over the edge of the etching bath. Alternatively a square plate with a long single strap can be used, which can be lowered into the tank to control the resistance. The cathode strip or square should be able to hang opposite the centre of the plate and be parallel to it. If it is not, the galv-etch may not be even in depth. To stop them being etched and prolong their life, seal all the metal crocodile clips, backs of plates, bars, straps etc. with ethanol varnish, or a strong stop-out varnish, leaving bare only those areas to be in direct contact with the plate. A grid cathode can be used in a vertical tank as well, unless you are using it for plating or galvanoplasty.

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©: May 14, 2015