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Chalkboards were black and later green.

The original chalkboards were black because they were made of slate. I'm not sure what the later green ones were made of. I think the green one's came about because slate got too expensive.

The markerboards are a very light grey, close to being more of an off-white, which is why they are frequently referred to as whiteboards.

A bit of interesting history on the progression from slate blackboards to the green chalkboards to whiteboards.

https://www.theatlantic.com/technology/archive/2016/10/theres-no-erasing-the-chalkboard/503975/

Greenboards are actually paint on a substrate (I believe), although they could be some other substance other than slate, like an engineered composite. In the past I have actually rehabilitated blackboards by painting them with a 'blackboard' paint, which was just regular paint with a slight abrasive added to give something to abrade the chalk with.

What I really like are the electronic whiteboards that can actually generate a print and/or electronic file of what is written on the surface. As part of the job I had in the early '80s, we did a lot of device configurations and system design on whiteboards. We actually purchased a Polaroid camera to take pictures of the board so it could be erased to continue with the session. The goal is the same as always, but the process and tools have sure changed.

Greenboards are actually paint on a substrate (I believe),

The article I linked to has that information.

Green chalkboards first appeared in the 1960s. Generally made of porcelain enamel with a steel base, these chalkboards are lighter and more durable than slate, and thus easier to ship. They were ubiquitous in American classrooms for three decades, until whiteboards began to replace them.

Slate is a material and a colour. Most often blue-grey, but slate does vary in colour.

Slate is a material and a colour.

In this case, the material is what is being referred to.

In this case, the material is what is being referred to.

The answer is the same either way.

The answer is the same either way.

Yes, but slate is irrelevant to the question. The green chalkboards are not slate in either material or color and I was wondering about the green ones.

The green version is typically coated pressboard.

The green version is typically coated pressboard.

According to the article I linked to up thread, the ones used in schools are typically porcelain enamel with a steel base, not pressboard.

According to the article I linked to up thread, the ones used in schools are typically porcelain enamel with a steel base, not pressboard.

I've never seen those, only boards like Remus2 mentioned. Geez, those suckers are heavy if they get to a reasonable size! That's for the green boards.
Now the white boards I have seen in enamel. Just like you can use white board markers on your fridge :)

I've never seen those, only boards like Remus2 mentioned. Geez, those suckers are heavy if they get to a reasonable size! That's for the green boards.

Actually, thin sheet steel is likely to be lighter than pressboard on a per unit area basis.

It's not like they need to use something particularly thick.

You have enamel fridges?

I thought they were all made with plastic exteriors these days.

I'm sure there are plastic exteriors but most I know have an epoxy paint coating that is baked to harden it. It's very much like enamel which baked on the metal surface too. You can use most white board markers on baked epoxy paint too but make sure they don't have a solvent in them that damages the paint.

AFIK most refrigerators in the US are still sheet steel with enamel coatings. Otherwise magnets wouldn't stick to them.

AFIK most refrigerators in the US are still sheet steel with enamel coatings. Otherwise magnets wouldn't stick to them.

Yep, sheet steel with enamel or epoxy paint. I think enamel is considered higher quality but I'm not sure.

AFIK most refrigerators in the US are still sheet steel with enamel coatings. Otherwise magnets wouldn't stick to them.

200 and 300 series austenitic stainless steel is paramagetic. Some 400 series are magnetic. Our stainless frig is 400 series and magnets definitely stick to it.

ETA: Stainless is a misnomer. It gets the name from a passivation layer (typically chromium). It can in fact stain. In fact, the passivation layer is actually oxidized chromium.

I've got some 'stainless steel' garden tools and 'stainless steel' kitchen implements that have rusted :-(

Soak them in citric acid (ascorbic) to clean. You may have to scrub, but use a stainless brush to do so. There are commercial products for this, but I'll usually buy non-sweetened kool-aid lemonade and mix it to a paste consistency to do it. It's cheaper than the commercial products. After cleaning, rub them down with a lemon. This promotes the surface chromium to form the passivation layer. It also works for brightening up aluminum.

If you've ever watched a hibachi chef clean the grill, the above is why they use a lemon at the last step of scrubbing the grill.

It's a shame the article doesn't explain the terminology was changed to appease the woke mob,

It wasn't. The terminology change predates the woke mob (it goes back to the 1960s) and it happened because of the change from slate(black) boards to the green chalkboards which are porcelain over a metal substrate.

Then, it's borderline silly to hang a whiteboard over a built-in wall-to-wall multi pane blackboard

Not necessarily, blackboards were also replaced for health reasons: the chalk tended to spread across the whole classroom. I remember seeing chalk mist in the classroom after the board was just wiped and the sun was right at the windows. The chalk itself is rather harmless but nevertheless a foreign substance you should not inhale.

Those classrooms tend to have a sink right in the classroom for that very reason.

ETA: but yes, I now remember also seeing a configuration where there's relatively little (office type) marker board freestanding off to one side in addition to the huge old chalk wall, probably now ever used by the teacher for semi-permanent stuff.

Those classrooms tend to have a sink right in the classroom for that very reason.

Yep, if there's a sink you can use a wet towel but I remember when they only had a brush to clean the board. There a reason a lot of teachers back then had one of the pupils wipe the board :)

Yep, and quite often picking on an already bullied kid, ostensibly unintentionally, of course.

Are marker boards any safer?

For people no. Chalk dust is particularly bad for computers.

At one place, the workings were done on a computer screen then projected onto a suitable wall. It was before touch screens became common and a special device was required to do the writing and drawing.

You probably talk about overhead projectors, which used a foil with the writing or drawing projected to the wall.
The systems I've seen usually had a foil roll you could scroll through so you could preprepare your demonstration. I remember some printers could print on foil sheets so you could show PowerPoint presentations.
Later there were LCD overhead displays directly connected to the computer.

HM.

No, the writings and drawings were saved on the computer and could subsequently be printed off.

I now remember those devices, they had a far higher resolution than the early touch screens, apart from the awkward position when drawing on a touch screen. Didn't they use a special stylus for drawing on those tablets? I've never seen one either in use or in a computer shop, only ads and IIRC they were expensive.

HM.

The chalk itself is rather harmless but nevertheless a foreign substance you should not inhale.

The change to whiteboards didn't really reduce the health risks, because

wipe off dry erase markers are used

Wiping off a whiteboard may produce fewer dusk, but the paint used in these markers is unhealthier than chalk.

HM.

But the point is that the teachers were inhaling the chalk dust every time they cleaned the board. They don't inhale the chemicals in the dry erase markers because wiping the markings away does not create a cloud of dust to be inhaled.

But the chemicals in the markers do create a vapor that is inhaled.

Then, it's borderline silly to hang a whiteboard over a built-in wall-to-wall multi pane blackboard (sonetimes with hidden cabinets behind it, in installations that are, or soon will be, over a century old by now).

That depends on why it's being done.

The article I linked to says the switch to whiteboards was driven by the increase in the use of computers in schools which necessitated the elimination of the use of chalk. Chalk dust and computers don't go well together.

I'm amazed that no one mentioned the joy of being told to go outside and clap the erasers.

Joy? You had to check which way the wind was blowing. Even then it was a mess.

Joy?

Yes?

Try getting writing on a whiteboard off after it has been there for a while!

There's actually a fairly easy fix for that and for someone accidentally writing on a whiteboard with a permanent marker. Trace back over it with a fresh dry erase marker and wipe off immediately.