By "uncial" we mean the text uses all capital letters, no spacing between words and no punctuation marks. Such conventions (spacing, punctuation, and lower case letters) are a relatively recent phenomenon in writing history. These have been found written on two types of media: parchment (sheep skin) and velom (calf skin).
267 Uncial documents containing portions of the New Testament have been found to date. This class of manuscripts dates to within a few hundred years of Christ.
When comparing Uncial texts with the rest of the documents that serve as the basis for Bible translations today, they are virtually identical!