I’m a hinge with no door, at the middle I bend. I help you wave, scratch, push or lend.

I tell you the worth I grow beneath the earth I get color from the Dutch But I'm nothing but a cut

I stand guard in a pitiful place; Gelatinous fortress, an arid embrace. I fight a foe that you cannot see, but another sense is glad for me. I fade each day, a duty unsung: Yet without my touch, civility's stung.

I show what’s in front, but I’m not what you see, I change with the light, yet stay just as I be, I vanish when touched, but never truly flee.

I break into your property at your command, Just to help you make sure no one else can. Who am I?