Ok, thanks Luigi.

 

This is how I sorted it out, hope it may help someone. It looks like I should write a typescript and a symbol definition file, but I new to this and don't know how to do it yet.

 

This is a workaround for the meantime:

 

- Download the free True Type font "Zapf Dingbats BT" from http://www.ufonts.com/fonts/zapf-dingbats-bt.html

- You should have got the file ufonts.com_zapf-dingbats-bt-2.ttf or an EXE file -an installer-

- In windows 7 it may be installed by clicking "install" -context menu, right mouse click-

- Generate Context font database:

 

mtxrun --script fonts --reload

 

- Check it's been read:

 

mtxrun --script fonts --list --all --pattern=zapf*

 

- You should have several lines like "zapfdingbatsbt    zapfdingbatsitcbybtregular       c:/windows/fonts/ufonts.com_zapf-dingbats-bt-2.ttf"

- Finally this is how I get the characters I need:

 

\definefont[zapfdingbats][ufonts.com_zapf-dingbats-bt-2.ttf at 10pt]

 

\starttext

 

Testing: {\zapfdingbats \char109}  %shadowed white circle

 

\stoptext