From "Iittala: 125 years of Finnish Glass, Complete History with all Designers"
From the Sarpaneva catalog (From the i-glass series):
Bird Bottle (straight) i-400
=2500
1956
i-colors
mould blown, flared
75cl
1957-1966
Bird Bottle (round) i-40
0=2501
1956
i-colors
mould blown, flared
50cl
1957-1966
From the text:
"A new concept for Iittala's household glass production came from the i-glass designed by Timo Sarpaneva, which reached the market in 1956. It created around it an atmosphere of discreetly aesthetic pleasure. The series was described as a combination of art glass and household glass. Sarpaneva and engineer Keijo Laitinen had developed new colors for i-glass—grey and a grey tinted blue, green and violet.. These became Iittala's stand colors for years to come."
I have one of each, one in green one in blue. Which is rarer, I can't say. The violet is particularly nice, I think.
Congratulations on your find.
Rob