Sealant PenWhite Caulk Marker: Waterproof Silicone Colorant Paint, Stain Remover, Sink, Kitchen, Shower, Bathroom Tile - White, Wide 15mm Tip

This seems really good from what we can tell other test we have done. My son has yet to do the whole windows

Works well, need to use it every few weeks or so but it does a good job of covering black marks. Happy with this product

Helps brighten up your seals.

Doesn't work if you hold it sideways only if facing downwards. The tip fell out of the end and splattered paint all over the floor, badly designed!

I didn't have issues getting the product to mix or flow out the nib - quite the opposite. The nib is massive, which makes for awkward application that doesn't reach into right-angled sealant. The product goes all over the surrounding surfaces which requires a lot of cleanup, not what I was expecting. Not precise application at all, with product flowing too heavily out the huge nib.

Works like a dream

This is very poor. Takes an age to actually get the paint flowing and the 'nib' is huge. Far too big and cumbersome to actually cover the sealant. The paint went everywhere but the sealant. The nib is also hard so it is difficult to press into awkward areas. When I did manage to get a small amount on the sealant (using a paintbrush) it was so sheer it didn't really cover anything at all. Don't waste your money, easier and cheaper to just replace the old sealant!

Applicator not suitable for joins and corners. Although I cleaned the surfaces, the whitening did not cover dark sealant. Leaks all over the utilities and tiles which then must be cleaned off. Reminded me of what you use on white trainers. Possibly okay for very small area coverage.