illustrator techniques: use custom brushes to create a custom border or frieze
The technique of making a custom border in Illustrator is similar to specifying a pattern. View the example starting motif and the finished border.
Start with a linear pattern that you wish to repeat seamlessly. I found this albatross motif which I (hand) traced in Illustrator.
And generated at least one instance of a seamless repeat by copying and pasting and filling in the missing segment.
First, make sure all of the elements of the motif are grouped together: Select > All and then Object > Group
This will also place all of the objects on the same layer.
Make sure the rulers are visible: View > Show Rulers
Find the edges of the repeat and drag guide lines from the vertical ruler to align with each of the edges. Try to be precise so there are no gaps or overlaps in the repeated design.
Make sure the guides are locked: View > Guides > Lock Guides. Make sure there is a check mark next to Lock Guides. Click to toggle the lock on or off.
With the Rectangle Tool (1), draw a box with no fill and no border (2) that completely encompasses the area to be repeated.
Select All again and choose Crop (1) from the Pathfinder panel (2).
This should result in a single instance of the repeat.
Note: If the original design includes complex appearances or blends, you may have to expand the appearances (Object > Expand Appearance) or expand strokes and fills (Object > Expand…) before cropping.
Select All again and open the Brushes panel (1). Make a new brush (2) and select New Pattern Brush (3):
Frm the Pattern Brush Options dialogue box, name the brush (1) and click on the Side Tile indicator (2) and click OK:
To test the repeat, use the Pen Tool (1) to draw a straight line (2):
Select the line. From the Brushes Panel (1), choose the new custom brush (2):
To change the size of the border, first select Object > Transform > Scale…
From the Scale dialogue box, make sure Scale Stroke & Effects is checked:
With the line segment selected and holding down the Shift ket, pull the upper corner handles out: