Hi Nathan C
Many thanks for taking the trouble to reply to me. I took another look, and there certainly does appear to be a border around the edge of the image in the slice. That would explain the gaps when using the image to create a custom brush. I tried playing around with the handles, making the image overlap etc etc, but I always seem to end up with the gaps.
When I just exported the artboard directly to png without using the export persona or creating a slice, it worked perfectly. So the issue appears to be with the slice creation, unless I am doing something wrong obviously. That is highly likely since I am very new to using this type of application.
As I have already found what is to me a perfectly acceptable work around, I can't see myself getting into a screeching rage about this! I was merely curious to see whether this is an inbuilt issue with the slices, or down to me being inept. I'm perfectly willing to accept it is almost certainly the latter!
I have attached a copy of the afdesign document with the artboard and slice so you can take a look if you so wish. I deleted all the other artboards and stuff not related to this query, so it's all easier to see. I'd be very interested to hear the cause of the 1px border, or what it is I am doing wrong, so that I can avoid it in the future.
Thank you again for taking the time and trouble to help me.
AvenueForBrush.afdesign