Phosphoric acid, (Part B for the two part teak cleaner kits) is commonly used used for darkening teak from white back to its brown color, can damage the pigment in Awlgrip. I have done it myself...bummer.
First, don't use the acid in high concentrations....try a very dilute concentration first, even if you end up having to acidize the teak twice. Second, rinse it off immediately. Don't let the acid sit for long and especially don't let it dry on the Awlgrip.
You will need to give the teak a light sanding
before varnishing regardless. You want the wood looking perfect before varnishing and you want the hard grain and the soft grain of the wood to be at the same level. Chemically cleaning
teak takes away more soft grain than hard grain, leaving the hard grain noticeably higher after varnishing.
If you are going to varnish
, then you may want to forego the chemical treatment and sand down to clean, level, unoxidized wood. Be sure to mask off the edges so you do not accidentally damage your paint
with sand paper.