What is this substance around the sink cutout in countertop?

[AlSailor]

I am replacing a rusted bathroom sink. After removing the old sink, I see that there is some substance covering the edge of the sink cutout. What is it?

Thanks.

 

[BMWpowere36m3]

Dried up plumbers putty, mastic, compound.... Does it really matter? Just seal the new sink with silicone.

 

[Sponsor]

 

[AlSailor]

So it's not necessary to coat that edge with anything? Just seal the sink with silicone caulk?

 

[Sluggo]

So it's not necessary to coat that edge with anything? Just seal the sink with silicone caulk?

No, it's not necessary. If the new sink has a lip that will sit on top of the existing counter all you need to do is put a bead of silicone on the top surface of the tile, set the sink in place and remove any squeeze out. No need to add non-functional glop to the area where you have the old residue. I have no idea why that old crap is there, but it wasn't necessary originally and it's not necessary now.