Returns content of the Blob base64 encoded.

A String value.  

object.ToBase64

The ToBase64 Method syntax has these parts:

The ToBase64 property will return a BASE64 representation of the data currently contained by the Blob. It is most often used because it is easier to represent binary data in this way for transfer by text-only services, such as email.

To get BASE64 data back into the Blob, you should use the FromBase64 method.

You can use this method as easily as this:

Dim b As New MemBlob
b.Text = "sometext"
Debug.Print b.ToBase64

result:
c29tZXRleHQ=