I don’t know the title of the book, that’s what I am seeking. It is a series book (Bobbsey Twins? Nancy Drew?) and the mystery involves the theft? Copying? of unique designs a jewelry maker obtains by capturing individual snowflakes on a pane of cold glass.
I think the setting is a winter lodge of some sort where the sleuths are vacationing.
I remember that the sleuth(s) are rewarded at the end with snowflake jewelry from the designer. I would have said a pre-1980 Nancy Drew as well, but I’ve been looking through the plot descriptions and can’t find anything that matches. I’ll keep trying!