meaning of this figurative sentence

[jesson cui]

As there are degrees of hardness in the hardest metal, and shades of colour in black itself, so, even in the asperity of Mrs Clennam's demeanour towards all the rest of humanity and towards Little Dorrit, there was a fine gradation. from Little Dorrit

i cannot apprehend this sentence clearly.anyone can help me? many thanks.

[Raymott]

As there are degrees of hardness in the hardest metal, and shades of colour in black itself, so, even in the asperity of Mrs Clennam's demeanour towards all the rest of humanity and towards Little Dorrit, there was a fine gradation. from Little Dorrit

i cannot apprehend this sentence clearly.anyone can help me? many thanks.

1. there are degrees of hardness in the hardest metal
2. there are degrees of blackness in black itself
3. there are degrees of asperity in Mrs Clennam's demeanour towards people.
Just as 1. and 2. are true, so is 3.
So, even given Mrs Clennam's asperity, her demeanour towards Little Dorrit had degrees/fine gradations.