Nice job, kra.
I think that the original mirror design was cut into the mirror from the back.
It would be done using a glass cutting wheel, which "carves" for want of a better word the design into the glass , and then silvered after that.
The fact that its carved gives various angles which reflects light when silvered.
This can not be achieved unless its cut on a wheel.
From the pictures it seems like you masked off from the front and sandblasted the design.
The other option is to acid etch the design on the mirror, this is an acid paste which instead of sandblasting the design area, is spread on the mirror to etch into the glass, this is a bit slower, but the finish is softer than using the sandblast method.
The back of the mirror is made up of two parts, the first is the layer of silver, which is a mixture of chemicals, using a double headed sprayer which mixes the chemicals before they hit the glass, and then its washed down using distilled water.
The second part of the back is a layer of paint that protects the surface of the silver.
If you choose to sandblast from the back both layers will have to be cut through, until you reach the glass itself.
I really dont think the effect is any better than what you are doing from the front.
Going through the back, looks basically the same plus you have to seal where you took away the protective layer of paint, which is important because if moisture gets at the layer of silver it will damage it. You could use a layer of clear varnish on the sandblasted area.
Either method you use will never look the same as the original mirror. Sandblast or acid etch eats into the surface layer of the glass, and it cannot reflect light.
The only way is cutting into the glass with a cutting wheel and then silvering the area. If you are thinking of doing that, its easier to use 6mm float glass and then cut the design into it, if you use mirror you cant see where the cutting head is , and then get the glass slivered.
We use a CNC to do the cutting, which is basically a giant computerised mat cutter, some of the cuts could be compared to v-grooves in mats, and then silvering the glass.
BTW The frames are stunning!!!