http://en.wikipedia.org/wiki/Faradays_laws_of_electrolysis
Faraday’s 2nd Law of Electrolysis – For a given quantity of electricity (electric charge), the mass of an elemental material altered at an electrode is directly proportional to the element’s equivalent weight. The equivalent weight of a substance is its molar mass divided by an integer that depends on the reaction undergone by the material.
Mathematical form
Faraday’s laws can be summarized by
m = (Q)/F) x (M/z)
where
m is the mass of the metal deposited at an electrode
Q is the total electric charge passed through the metal solution.
F = 96,485 C mol-1 is the Faraday constant
M is the molar mass of the metal which is 107.88 gm/mol for silver
z is the valency number of ions of the metal ( 1 in the case of silver)
Note that M / z is the same as the equivalent weight of the metal deposited.
For Faraday’s second law, Q, F, and z are constants, so that the larger the value of M / z (equivalent weight) the larger m will be.
In the simple case of constant-current electrolysis, Q (coulombs) = electric current in amps (coulombs/second) x time t (seconds)
For a 4 x5 inch plate (area 129.032 cm2), a 10 micron (.001cm) layer of silver (10.49 gm/cc) weighs .000134535 grams.
.000134535 grams of silver contains m / 107.88 or .00001254677 moles of silver
which when multiplied by Faraday’s constant (96485 Coulombs/mole) will require 1.210575 coulombs of electircal charge.
Assuming a reasonable plating time of 5 minutes or 300 seconds, a current of .00403525 amps or 4 milliamps will be required.
Therefore you need to get yourself an accurate milliamp meter to monitor this current plus a DC rectifier or battery current source.