Long story short, Noodler's Ink is switching from glass to plastic bottles for their 3oz fountain pen inks because of supply constraints, at least for the next several months.
Stock will be mixed -- we'll do our best to update product descriptions on our site, but we may not be able to guarantee anything. The plastic bottles should hold slightly more ink, so that will provide even more ink value for you in the interim.
As of this blog post (August 19, 2015), we don't have any of the plastic bottles here but we expect to see a transition in the next few weeks depending on the distributor's supply. The 1oz and the 4.5oz bottles shouldn't be affected.
Thanks for your understanding!