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#1 Post by MicroMan2 » Thu Nov 02, 2017 5:40 pm

When I make crystals for observation I usually add the solute in a water/alcohol solution and let evaporation takes it course. My question is when crystals are made this way do I have to cover it with a coverslip to preserve it or can I leave it out in the air after evaporation is done?

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Crater Eddie
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Re: Crystals

#2 Post by Crater Eddie » Thu Nov 02, 2017 6:06 pm

I think that might depend on what the crystals are. At any rate I would keep them covered somehow to prevent dust and damage.
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Re: Crystals

#3 Post by Hobbyst46 » Fri Nov 03, 2017 2:28 pm

May I add here some points.
From what you describe, crystallization occurs as the alcohol (presumably ethanol? or methanol?) evaporates, your solute is better soluble in alcohol than it is in water, so the aqueous phase becomes saturated and as water evaporates as well, crystals start to form.

I would keep the crystal products in a tightly-stoppered vial, to protect it from atmospheric humidity effects. Relative air humidity goes up and down on daily and seasonal basis, depending on the temperature and preciptiations. A high relative humidity is liable to cause partial dissolution of the crystal phase and deform it. Thus, what was initially a smooth surface, may become porous. That might affect its optical features.

Moreover, I would stop the crystal growth before it has dried. I would avoid having all the liquid evaporated. Better stop the process and harvest your crystal when it is still submerged in liquid. Pull it out of the jar and wipe gently. Again, this way may eliminate surface imperfections and "twins". Best crystals are obtained under steady state. A partial drying step may interfere with the form.

Good luck.

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Re: Crystals

#4 Post by billben74 » Fri Nov 03, 2017 9:56 pm

I think Microman 2 means that he puts the ethanol/water solution, nearly dry, but not quite onto a slide and then observes?

Microman2 is then asking about how to make this permanent

I mainly use water, sometimes other solvents - it depends on the solubility of the crystalising substance.
I also do "melts" when the substance has a fairly low melting point e.g. ammonium sulphate (amazing stuff by the way) - 243 C.
Put the substance on the slide, put a coverslip on top (if you want) and then heat - I use my gas hob.
Slide glass is fairly resilent - I havent cracked on yet.

I personally don't try to make permanent crystals slides. The evolve over several days and a lot of the fun is watching this process.

Of course this does mean they tend to degrade to a sort of white out effect -> but this does depend on the substance (and probaly solvent).

I normally use a coverslip but have experimented not using one -> it produces interesting 3-d effects of course as the crystals grow in 3 dimensions. This can reduce sharp focus but the effects can be fascinating.

One could seal a coverslipped slide with nail polish etc (I presume) and this should slow change and in time may become permanent.

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