Making lava at home

My 7 year old wants to make lava. I have a small forge that can go up to approximately 1,800F. So, my thinking went, I could put some easy
to melt rocks into a ladle and melt them, that would become lava.
It would be an educational backyard fun, as long as no one sticks fingers into anything hot.
The question is what rocks would be a easy source for making lava.
My first thought would be to go to Home Depot and buy some lava stone that they use for landscaping, but I am not sure if it will melt at my forge temperature.
I need roughly one pound of that stuff. I also want something that does not have air or water trapped in it that would be prone to any sort of explosions.
Any ideas?
i
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On Tue, 28 Apr 2009 19:25:27 -0500, Ignoramus23032

Use glass.
Regards,
Boris Mohar
Got Knock? - see: Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca
void _-void-_ in the obvious place
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Silica sand, glass.
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I have some black glass grit for blast cabinet, this would seem to be the safest route to take. Thanks a lot.
i
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Iggy,
I assume that after you melt it you want to pour it over something so it can flow downhill and cool into lumps and rocks? With glass I'm afraid that you will get all kinds of internal strains and the lumps will be very prone to shattering. You definitely don't want glass fragments flying around. How about using table salt instead?
----- Regards, Carl Ijames

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Salt is even better, melting point only 1480F or so. I like it.
i

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Ignoramus23032 wrote:

Do you have a temperature controller on the furnace, if so then you could pour the glass over something then let it cool and place it back in the furnace to anneal. The glass pieces I blow are placed in a lehr and held at about 500C until the blowing day is finished then the lehr slowly brought down to room temperature overnight to prevent stress being built up in the glass. IIRC above the strain point, about 500C for the glass I use, you cannot induce permanent stress in the glass. Below that point you need to cool the piece slowly enough that damaging thermal stresses aren't created. The thicker the glass the longer the cooling cycle.

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On Tue, 28 Apr 2009 21:57:11 -0500, Ignoramus23032

Even though you now seem to be headed towards glass/slag etc. I felt I should belatedly leap in an warn about using salt.
Two issues with salt.
One is for stuff in the workshop, A salt bath spits enough finely divided salt "smoke" into the air to make rust spots appear on steel objects all around the shop DAMHIKT.
The other is that when the salt melts it has about the same viscosity as water. This is a Really Bad Idea(tm) for lava making, although dead handy when used in a crucible for hardening steel.
The other, other point (ok, three) is that the salt fumes in an electric forge will destroy the protective oxide layer on the heating elements and lead to rapid failure. Luckily I just got all of the hardening job done before I discovered this...
Mark Rand RTFM
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The other - broken pyrex glass. That is high temp glass and resists stressing. It might work.
I have tons of lava rock - round rocks 1/4" diameter as a road base. Martin
Carl Ijames wrote:

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Is that real lava rock or slag? (both should work well)
i

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They are finger tip size small balls of volcanic exploding and creating a bed of 'gravel'. Some float due to trapped air and some are filled. Black green glass.
Martin
Ignoramus23032 wrote:

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That's borosilicate glass----melts at a much higher temperature than 1800F.
Harold
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Tim wrote:

Add some soda and lime, which depresses the melting point of silica.
http://www.ecu.edu/glassblowing/oldrecipes.htm
Cheers
Phil Hobbs
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On Apr 28, 5:25pm, Ignoramus23032 <ignoramus23...@NOSPAM. 23032.invalid> wrote:

Iggy. All the rocks you will find in your area contain water that will turn to steam and explode when heated rapidly. Please use some of the actual lava rocks you wrote about and first heat them for an hour or more in a hot oven to drive the moisture out. May need to do this several times. Your local rocks are basalt and will take forever to get the water out. Exploding rocks are not funny! They are very dangerous.
Your 1800 degree forge will just get the rocks red. The will not melt. A quick Google search shows lava temperatures of 2200 degrees F.
I think the glass suggestion will be a better choice.
Paul
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Add borax (even the 20 Mule Team stuff) to dramatcally lower the melting point and viscosity. Or you can just melt the borax alone.
23032.invalid> wrote:

Iggy. All the rocks you will find in your area contain water that will turn to steam and explode when heated rapidly. Please use some of the actual lava rocks you wrote about and first heat them for an hour or more in a hot oven to drive the moisture out. May need to do this several times. Your local rocks are basalt and will take forever to get the water out. Exploding rocks are not funny! They are very dangerous.
Your 1800 degree forge will just get the rocks red. The will not melt. A quick Google search shows lava temperatures of 2200 degrees F.
I think the glass suggestion will be a better choice.
Paul
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I do not know for sure, but I would try to find some slag at a dump for a blast furnace.
Bill
--
Most people go to college to get their missing high school education.

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That slag is also sold at Home Depot as some fancy shmancy "landscaping" rock. I like it a lot. I think that I will buy a bag of that stuff, as I could use it for anything I want. Then I will put a couple of lbs in a grill for 1-2 hours, and I will be good to go. It is more lava like than salt.
i
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RCM only
On Tue, 28 Apr 2009 23:21:27 -0500, the infamous Ignoramus23032

Ig, when I was your kid's age, we got the little black pellets on the 4th of July. I think they were called "worms" or something. Anywho, you'd light the top and they'd glow red, sulfury-smoke a lot, and foamy slag would form on top which wormed its way out and down. If you could find those, I'm sure he'd be happy and they're MUCH safer. Kids'll be kids, and the thought of what would happen when a rock got thrown into a pool of real lava gives me the creeps.
Just a thought.
------------------------------------------------------ No matter how hard you try, you cannot baptize a cat. ----------------------------
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wrote:

You can get a eutectic mixture of sodium and potassium salts that has a melting temperature around 1200 or 1300 deg.F. IIRC.
This stuff is available commercially for salt bath heat treatment furnaces.
When red hot this salt becomes conductive and may be heated further by passing a current through it.
Wolfgang
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That novelty thing is exactly what I was thinking of, and it hasn't been too many years since I last saw them.
--
WB
.........
metalworking projects
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