HOW TO RECOLOR AN ASTRACAST GRANITE SINK. IT IS BLACK AND 12 YRS. OLD

i have a black astracast granite sink,. It is 12 yrs old and the black color is fading on the bottom of the sink., Someone told me to put shoe polish on the entire sink., I did this and it looks super, almost like new. But what could I put over the shoe polish to keep the color from washing away. Thank

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