sympathetic ink meaning in English

【化学】(起初无色后来经过某种作用才现色的)隐显墨水。

I grasped it in my hand , put out the flame as quickly as i could , lighted my taper in the fire itself , and opened the crumpled paper with inexpressible emotion , recognizing , when i had done so , that these characters had been traced in mysterious and sympathetic ink , only appearing when exposed to the fire ; nearly one - third of the paper had been consumed by the flame
我吓了一跳。赶急把那张纸抓在手里，扑灭了火，直接点燃了那支小蜡烛，然后带着难以表达的激动心情摊开了那张扭皱了的纸。我发觉那上面的字是用神秘的隐显墨水写的，只有拿到火上去烘才会显现出来。