Australia's Science Forum

I asked a teacher to use plastic containers to mix the Plaster of Paris, she used glass beakers and let the waste set in them. I cant get it out. I have tried hot water and now am about to try acid. But does anyone know how to dissolve it before I go ahead?

Sorry I can't help you there.

Why would anyone think to do that... really?!?!?

Have you just soaked them in water? Maybe leave it overnight.

maybe throw them out and charge teacher for the cost of new ones- do NOT put yourself at risk of broken glass by trying to clean them out..

Soaking in water (soapy) for a day or so (possibly three) should soften up the plaster enough to be able to either chip it away gently from the beaker using a metal spatula, or if softened enough just wipe it out with paper towel. Just make sure that you do not put the solid waste down the sink.
P.S. (Some teachers were just sent to try our patience.)

I've done the soaking but not with soap. Will give it a go.The acid doesn't appear to work. And I was going to try drilling it out to break it up. The teacher misheard me and is majorly apologetic.

A few years back I had one that wanted to do a full hand cast then split in half with a chisel and hammer. Not to mention it can cause burns during the setting process.

Just went to put this away .The label says Chem supply Plaster of paris.
Chemwatch says this is non hazardous and there are therefore no phrases or GHS symbols . The Chemwatch MSDS is 2013
As the original label is not on the container I have no way of telling who the real supplier was .
Other suppliers of Plaster of paris ( calcium sulfate ) do have a warning and several risk and hazard phrases .

I come across this situation all the time where the original supplier is not listed and I have to make a choice. Often some have associated Risk phrases and some don't .

So is it a case of if in doubt print a label that has Risk/Hazard phrases ( and obviously is GHS ) or trust the one that is on it to be correct

This wouldn't be the first time that someone has found inconsistencies with Chemwatch SDS/labels! Have a look at their safety data sheet - I have come across ones that have a title and right through the whole sheet it says "not applicable" for every category. I now no longer rely on Chemwatch for SDSs because I do not have confidence in what they say.
If you are not sure who the supplier is, but are definite that it is plaster of paris, I would rely on information from a supplier of a similar material.
When in doubt, go with the information that has the higher risk. Better to over-kill than under do it.

Perhaps drill a few small holes in the plaster with a battery powered drill on a low torque setting, to release tension; though that may be tricky not to break the glass. Then screw a self tapping screw into the plaster then pull on it with pliers. Note: I have never tried this method.

How much is each beaker worth?? How much time and effort have you already put in???
Throw them out!