Thin item of laboratory glassware able to withstand high temperatures (4,4)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
test tube
(Other definitions for test tube that I've seen before include "'Laboratory glass cylinder (4,4)'" , "used by chemist" , "Item used in chemical reactions" , "useful for experiment" , "Container for precipitation" .)