We present the most continuous data base of optical BVR _ { c } I _ { c } observations ever published on the BL Lacertae object GC 0109+224 , collected mainly by the robotic telescope of the Perugia University Observatory in the period November 1994-February 2002 .
These observations have been complemented by data from the Torino Observatory , collected in the period July 1995-January 1999 , and Mt .
Maidanak Observatory ( December 2000 ) .
GC 0109+224 showed rapid optical variations and six major outbursts were observed at the beginning and end of 1996 , in fall 1998 , at the beginning and at the end of 2000 , and at the beginning of 2002 .
Fast and large-amplitude drops characterized its flux behaviour .
The R _ { c } magnitude ranged from 13.3 ( 16.16 mJy ) to 16.46 ( 0.8 mJy ) , with a mean value of 14.9 ( 3.38 mJy ) .
In the periods where we collected multi-filter observations , we analyzed colour and spectral indexes , and the variability patterns during some flares .
The long-term behaviour seems approximatively achromatic , but during some isolated outbursts we found evidence of the typical loop-like hysteresis behaviour , suggesting that rapid optical variability is dominated by non-thermal cooling of a single emitting particle population .
We performed also a statistical analysis of the data , through the discrete correlation function ( DCF ) , the structure function ( SF ) , and the Lomb-Scargle periodogram , to identify characteristic times scales , from days to months , in the light curves , and to quantify the mode of variability .
We also include the reconstruction of the historical light curve and a photometric calibration of comparison stars , to favour further extensive optical monitoring of this interesting blazar .