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BASIC PROCEDURE IN GALV-ETCHING


using a standard tray and grid system

Fill the tray with electrolyte to the height of the bottom of the grid and then remove the grid. Lower the plate to be etched into the electrolyte by its strip contacts. If you are using a backplate contact, put it into the tray with the strip bent up at the right position for the edge of the plate, then lower the plate into the solution onto the centre of the backplate contact. Place the grid onto the tray, with its wires just immersed in the electrolyte. At this stage make sure that the battery charger is switched off, either at the mains, or by a switch or timeswitch on its output

Attach the positive (red) terminal of the battery charger to the plate contact strip or the backplate contact, and the negative (black) terminal to the grid or cathode. Check that you don't have any short circuits - leads, straps or crocodile clips touching. Then switch on for a moment, and watch the ammeter and voltmeter to check that the current and voltage are OK and note the readings. If the needle goes off the scale, or the digital display shows above 10 amps or 5 volts, switch off quickly, lower the voltage setting and try again.

At this stage you may be calibrating your system with a test calibration plate, in which case follow the procedure detailed in the section on times and tests. If you are etching a prepared plate, calculate the time you need from the voltmeter readings (see section on times and tests). Then set the time switch, if you have one, leave it to etch for the required time. It is a good a idea to keep a record of what you have done on every plate.

If the ammeter reading is very high because the exposed area of your plate is large, then the voltage should be lowered by switching it a lower setting, or the resistance increased by switching in the control box , or by the other means described later (galv-etching very large plates). An uneven bite can be caused by the cathode grid or plate not being parallel to the plate and opposite its centre. There is a slight tendency for edges to bite more deeply than the centre, which can be counteracted by having the cathode grid slightly smaller than the plate if you notice a problem. Narrow open bite areas tend to bite more deeply than broad ones, something that can only be avoided by biting in short steps and stopping them out sooner. Similarly, isolated lines bite slightly more deeply than closely spaced hatching.
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up Photograph of setup with

(1) flat tray,
(2) backplate contact,
(4) grid,
(5) Velleman power supply, and
(7) timeswitch ,

open bite or galvanoplasty in a flat tray

A flat tray can be used for plating or open bite provided that you have some means of controlling the surge of current caused by the very low resistance of a plate with large areas of bare metal in the electrolyte. The control box shown in the diagram can be inexpensively made up from off-the-shelf components. Note that adding a resistance like this in series, has the effect of reducing the voltage over the anode and cathode (see section on times and tests). For plating, a grid (which becomes the anode) is not ideal as it is etched away and a solid plate can be attached to the underside of the grid.
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etching a plate in a vertical tank

A large tank requires a larger volume of electrolyte, but its greater width allows you to see the progress of the etch more easily and you can have more control over the distance between the plate and the cathode grid or plate. The cathode should be about the same area as the plate, and it should be hung directly opposite its centre. The tendency for lines or areas near the edges of a plate to be etched more deeply than the centre can be counteracted by making the cathode plate slightly smaller and therefore closer to the centre of the plate to be etched.

vertical tank
up Vertical tank with cathode plate and cradle contact to hold plate (anode) Note tap to empty.

When plating or deep etching large areas of open bite with a strong current (amperage) there is often some loose deposit produced, and the advantage of a vertical tank is that it does not drop back onto the plate, but sinks to the bottom of the tank. This can then be emptied and filtered and the clean solution returned to the refilled tank. If you don't have a tank with a tap, use a plastic tube as a siphon, and start the siphon going by holding it all under the electrolyte surface (with gloved hands) until it is filled with liquid. Then close both ends and take one end out and put it into the receptacle to store the electrolyte. Don't start the siphon by sucking the liquid up it. For storage I use plastic camping water storage jerry-cans, with taps.
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up Detail of deep etched zinc plate etched in vertical tank, printed in intaglio and over printed from the same plate in relief.

deep etch and open bite

Large exposed areas of a plate will increase the current required from the power supply, so to keep the current within the limits of the power supply's ammeter, the resistance can be controlled by lowering the voltage output of the power supply with the controls that you have. This will increase the time taken to etch, but will decrease the intensity of the etch per unit area. There is not usually any need to protect the whole of the backs of plates because very little electrolytic action will take place "round the corner" as it were. The ions in the solution are most strongly attracted to the nearest surfaces, which are the facing sides of the anode and cathode plates. This also makes it easier to make an electrical contact with the back of the plate, avoiding the need for crocodile clips and possible marks on the surface.
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