When it is required to be strengthened, it is only necessary to add a little of the sulphate of copper.
"With the battery prepared as above, and the solution of sulphate of copper in a vessel of proper dimensions to receive your plate, connect the galvanic current, and immerse the impressioned plate, letting it remain until a thin film of copper has been formed, then the battery can be strengthened, and the impression will be of sufficient thickness to be removed in from eight to twelve hours.

An old Daguerreotype plate attached to the opposite pole of the battery (copper side towards the face of the plate to be electrotyped), will answer the same purpose as the silver-plate.
"The great difficulty in taking an electrotype impression, and preserving the original, has been attributed to the battery being too powerful.

I am led to believe from practice that the principal difficulty has been in the Daguerreotype plate itself, for if we use an impression that has been taken but a few days, and taken in the usual way, we will find it difficult to succeed without spoiling both the copy and original, and so also with an old impression.
"I have found the most certain method to be as follows:--Coat the Daguerreotype plate as usual, except use less of the accelerators, the proportion of iodine coating being greater, of course the time of exposure in the camera will be lengthened.

Mercurialize it at about a temperature requiring to develop the image, from six to eight minutes, at least.

Gilding the Daguerreotype has much to do towards producing a good electrotype copy.