Making a Plaster cast

[Satu11]

Hello everyone,

During a science day this week there was an activity that involved making a plaster cast.Does anyone has any suggestion on how to make one. Mine did not work very well. Students had to make a hand print on the sand and then I had to pour plaster of pairs mix into the mould.I did mix100gm of plaster of paris in 70ml water which was written on container of plaster of paris under directions to use.I used wet sand. Some of them are not dry yet , some are cracking. How long does it take to dry and is there any other way to do it. The students hand prints were also not deep enough. My HOD says it should be fine.Any sort of feedback will be appreciated.

Thanks
Satu11

[lada]

Not sure. We use plasticine to make moulds of shells etc, than oil it little bit and pour plaster in it.
How about line the sand moulds with glad wrap?
Good luck
Lada

[Lyn]

Do a search for plaster and look on page 5, or check under artificial ore. I have posted how to mix plaster on the artificial ore site. The method for making up plaster was demonstrated to an art class in the mid 1960's and the art teacher was very specific as to how we had to make up the plaster without getting any lumps in the mixture. May be very old school but has always worked for me.
Lyn.

[nickykinz]

Warning – Graphic images

http://www.mirror.co.uk/news/uk-news/ar ... ght-424409

Here is a cautionary tale about plaster of paris and not doing risk assessments. Do not look if you are easily upset.

[curie]

Man, that is shocking .

[sunray18]

We rub vaseline over the shells.. this makes them easier to remove.

[Lyn]

We use paddle pop sticks to stir the plaster which is made up in 250ml plastic beakers. Have to admit those pictures show some dreadful injuries.
Lyn.

[RosalieM]

I agree this is a tragic story and I really feel for the girl who has suffered (and good on her for getting on with life), but this line really stood out to me:

"The horror happened after the youngster “misunderstood” instructions from her art teacher. She was meant to put her hands in nearby wet clay to make moulds."

The instructions were there. She was 19. I also feel for the teacher who most likely thought a 19 year old could follow instructions.

We do risk assessments, but we don't always tell the kids what could happen because in this day and age the kids are highly likely to see if it is true!

Eg. Teacher: "Don't put your hands in the plaster. It will get hot and burn you badly"

Student thinks: "Oh, really? I bet it's not that bad. Probably a bit warm maybe. I bet the teacher just doesn't want us getting messy. I'll put my hand in and see, and then prove how tough I am to everyone else."

While this is not a real scenario of what has happened at our school, it's how kids think. One day a senior class was testing pH and ammonia was one of the substances. Teacher says "put the lid back on quickly and make sure you don't sniff it." One student then said "why?" proceeded to open their bottle and have a good whiff. Ended up in sick bay and I think they got a bleeding nose out of it. Some kids just can't be told...

[mtg]

re hand accident: My MSDS only says slightly hazardous in case of skin contact??!! I've never had it set that quick either. Maybe they weren't using "dihydrate"?
We do a footprint prac in damp sand and the fossil prac with shells and damp sand. Mix the calcium sulphate dihydrate so it can be poured but not too runny, wait til it's set then brush off the sand. Handprints would not show more than size the way we do it.

[nickykinz]

I think the age thing was a bit misleading. Having read a couple of different articles about it I think she was actually 16 when it happened and this story was from when it went to court, by which time she was 19. And I don't suppose it became an issue until it started to set and got hot. It was a very unfortunate set of circumstances though and you can't predict every stupid thing a student could do.
I think the problem can be that it is such a commonly used product that the teacher may not have even realised it could be an issue. As you say the MSDS doesn't say it is hazardous or dangerous. Even "science" teachers sometimes say "well you can buy it at the supermarket so it can't be that dangerous" to me. However having your hands encased in it is different to splashing it on yourself. After I heard about it I just thought it is a good idea to bring this sort of story to the teachers attention so they can look out for that kind of thing.
And of course some kids are always going to do the wrong thing but if you have done a risk assessment and said "don't stick your hands in it" then you are less likely to get sued for it.

[nickykinz]

After having a look through the different MSDS's for different brands, some say hazardous and some say not, and some say goggles and gloves and some say you don't need to. They all have similar compositions though. In fact the Boral's MSDS for casting plaster says non hazardous but the Chemwatch version of Boral's Casting plaster says hazardous!

[bunsen]

WE make forensics foot print casts all the time here. Sand in a tote box and student walks on to leave print, wet or dry sand works, wet gives a little more detail however the sand must be totally damp not just the top surface as it will just stick to students shoe when stepped on. When you have your print get some long strips of cardboard from scrap cardboard boxes (approx. 5cm wide), I staple strips together to get them long enough. Curl strip to form a loop and staple ends together, the loop should be big enough to encircle your print when placed on top. You can now add enough plaster to make a thick enough cast. From my instructions to students: mix 65ml of water to 100g of plaster: One level 250ml beaker contains approx. 300g of plaster, so for every plastic beaker of plaster add 200ml of water. When casting other thinner casts I have added pieces of coat hanger wire or icy pole sticks as reinforcement.
Cheers

[Graham Kemp]

After having a look through the different MSDS's for different brands, some say hazardous and some say not, and some say goggles and gloves and some say you don't need to. They all have similar compositions though. In fact the Boral's MSDS for casting plaster says non hazardous but the Chemwatch version of Boral's Casting plaster says hazardous!

Plaster of Paris is a fine powder that reacts exothermically with water to expand into a hard solid. This alone should tell you to trust the SDS that say it's hazardous if applied directly to skin, mishandled, or if it reaches eye or lung. Take care.