I have three 12" Victor records, seem to be acoustic era. They are one-sided and seem to be made of 
a less-fragile material than shellac, some kind of plastic?

1. Victor Record 74163 Dvorak "Humoresque" - Mischa Elman with piano accompaniment by Percy B. Kahn. 
Deadwax says catalog number

2. Victor Record 74256 Pierrot's Serenade (Alberto Randegger, Jr.) - Jan Kubelik with piano 
accompaniment (pianist not named). Deadwax says catalog number

3. Victor Record 70073 Verdi  "Rigoletto" quartet - Bella figlia dell' amore (Fairest Daughter of 
the Graces) Act III - Victor Opera Quartet, accompaniment by Victor Orchestra. Deadwax says catalog 
number. On the back (blank) side is a sticker (seems to be paper) with descriptive text and lyrics.

So -- what is the era of these records and what are they made of and why are they one-sided?

Thanks!

-- Tom Fine