Recipes for Growing Sugar Crystals

Since I issued this website I got several requests for recipes to grow crystals, some asked especialy for recipes to grow sugar crystals.
It seems that the common recipes are only vague or not working sufficently.
One of the big problems growing crystals of sugar is its extreme high solubility and the high viscosity of its solution.
The good thing is its available anywhere, its cheap and its not poisenous.
If we talk about sugar we mean cane sugar as there are existing many kinds of different "sugars" which are all seperate "chemicals" like glucose, fructose, xylose, maltose etc.
Before we start something about units. Many of you may still be used to ounces, pounds, Fahrenheit etc. In spite the fact that I still use this units in this script sometimes I recommend strongly that you get used to metric units, its so much easier to calculate with them !
If you buy scales, measuring caps etc. make shure that they have metric units, too. That makes it easier to switch.

Physical and Crystallographical Properties

Either known as cane sugar when made out of sugar cane or as beet sugar when made out of sugar beets. Don´t be confused both are the absolute identical chemical compound. Sugar is one of the purest commercialy distributed organic "chemicals" produced in millions of tons. There is no need to buy analytical grade sugar for crystal growing experiments, its only something for scientists or if you have to much money. Just take the regular sugar from the next supermarket - watch for sales (sugar can not rot) !

Sugar crystal floating in a saturated solution. Crystal size app. 10 mm, picture taken in polarized light

How to grow sugar crystals from a solution in water

There are two simple basic methods to grow crystals from a solution

• The Evaporation Method
• The Slowly Cooling Method

Using the evaporation method you simply let evaporate the solvent (e.g. water) of your saturated solution to get crystals.
Its quite simple but may take a long time. If the solubilty is low you may wait a very long time to get nicely sized crystals. Fortunately in the case of sugar the solubility is very high.
Using the slowly cooling method you produce a hot saturated solution and let cool it down slowly to get the crystals.
The catch is let it cool down slowly.As slower a solution cools down as bigger and finer the crystals will be. The second catch it does not work with substances which do not change solubility greatly with rising temperature (like regular table salt) or which´s solubilities go down with rising temperatures.(this is not very common but shit happens). Fortunately the solubility of sugar rises greatly when the temperature goes up.
The good thing is this method is quick you will get nice sized crystals within several hours to days.

The Evaporation Method

Disolve per 100 gms of water 230 gms of sugar heat up the solution until it boils and gets clear. Then if you want filter trough a regular coffe filter with paper. But filtering is not absolutely necessary. The solution may have a slight yellow hue. For heating up the solution use a cooking pot or a vessel made from heat resistant glas (pyrex), as for example replacement jars for electric coffee machines. You may also use the microwave but of course only use vessels which are suitable for this (no metal or metal parts !).
To grow the crystals you can use any kind of glas or plastic container with a wide open mouth. For example preservation glases etc. You should produce at least about 500 ml of solution better arround 1000 ml (or a quart). For a method how to calculate a specific volume of growing solution see the "Calculating a Solution" part down below.
After the covered solution has cooled down so after two or three days there should be some sugar crystals at the bottom of the jar. If not throw in some little grains of sugar. Let the solution stay alone and covered for about a week.
If you got no crystals on the bottom, yet even after throwing in some sugar grains your solution can not be saturated and wan´t work.
This may happen either because you made a mistake with the amounts of water and sugar used or your room temperature is well above 20 °C (app. 70 °F).
To avoid mistakes in the amounts of water and sugar used, use an electronic kitchen scale wich should have at least a resolution of 2 gms (better 1 gm) most can be switched from oz./lbs to metric, metric is easier to calculate. Also weigh the water as its much more accurate as measuring the volume.
If your room temperature is well above 20 °C you have to adjust the initial recipe. If you look at the solubility table down below the solubility of sugar at 20 °C is 203 gms per 100 gms of water. In the recipe we took 230 gms (27 gms added as security gap). If you work for example at a room temperature of 30 °C you adjust the recipe to 250 gms per 100 gms of water (again app. 30 gms as security gap).
Okay everything worked fine, there are some crystals at the bottom and the solution rested for a week. Now pour the solution in your final freshly cleaned growing vessel. You may filter but its not absolutely necessary and filtering the viscose solution may take for ever.
Now you need a seed crystal, usualy you will find at the bottom nicely sized sugar crystals already suitable for this purpose or you may use a bought candy sugar crystal (that´s cheating !). Dry up the crystal with some paper towel and fix it with a slip knot to a thread of "invisible sewing thread" which is a thin clear thread of nylon or use very thin fishing line. Don´t use regular threads made out of cotton etc. as they work like a wick and are easily visible in the ready crystal.
Fix the thread to a pice of wood or a pencil for example so that the crystal suspends somehow above 2 - 3 cm (about one inch) the bottom of your growing vessel but well below the surface of the solution. Before doing that rinse the crystal on the thread shortly in cold water.
The growing vessel must stay open to allow the water to evaporate but you may cover it with a thin paper towel (most paper towels are multi layer so you may split them) to prevent flies, wasps, dust etc. from falling into the solution.
As the water evaporates your seed crystal will grow.
This will not work if you are in a very humid climate or if your room temperature changes and goes up.
As evaporation goes on there may grow additional crystals on the bottom of the vessel on the thread or on the sides. They grow on the cost of your desired main crystal. If so, pour the solution in a freshly cleaned other vessel rinse the crystal and the thread shortly in cold water (remove additional crystals which may have formed on the thread) and go on with evaporation.

Fixing a seed crystal to a thread with a slipknot	There is not enough solution in this growing vessel	Additional crystals at the bottom grow on the cost of your main crystal !

The Slowly Cooling Method

If you produced the saturated solution for the evaporation method and found some crystals at the bottom you already used the slowly cooling method to produce crystals ! To get bigger and better ones you just have to add more sugar (larger "security gap") and take care that the solution cools down very slowly.
A good basic recipe is to add 230 to 300 gms of sugar to 100 gms of water, heat up until the solution boils and gets clear. You may filter if you want but its not absolutely necessary. Pour the solution in your final growing vessel and close it tightly. Take care that the the solution cools down very slowly by insulating it and also avoid any moving, shaking or vibration of the solution.
You may give the crystals a better surface to grow, a matrix, if you put in a piece of rock, or have it suspended on a thread, or use a metal paper clip on a thread.
It takes a few hours to days, depending on how much solution you take and how good your insulation is, until the solution has cooled down to room temperature and the crystals are ready.
They main problems you may have with the slowly cooling method is that the solution does not cool down slowly enough, which results in small crystals or your solution has cooled down but there are no crystals at all !
What happened ? Supersaturation ! Your solution contains much more sugar as "allowed" since there have not formed any seed crystals spontaneously. If the solution is disturbed or you throw in some little sugar grains crystallisation starts immidiately.
Since the growing velocity of sugar crystals is small, solutions are often slightly supersaturated when they have cooled down and so the crystals still grow a little while even if the temperature does not change anymore. So allow the crystals some extra time.

The Trick with the Thermal Ballast

As more volume of solution you have as longer it will take to cool down. The reason is that the surface of your vessel is growing by power of two but your volume and so the amount of heat energy is growing by power of three if you enlarge the dimension of your vessel. The heat loss depends on the surface area available. To give you a simple example lets say we have a cubic container of 1 inch, so the surface is 6 square inches and the volume one cubic inch. Now lets take a container of 10 inches size the volume will be 10*10*10 = 1000 cubic inches but the surface only 6*10*10 = 600 inches. With the small container you have a volume/surface ratio of 1 to 6 with the big one a ratio of 10 to 6 and its a good guess that cooling down takes ten times longer. So that was the physical principle !
However who wants to handle gigantic amounts of solution just to grow some little crystals ? Nobody told you that all of the volume must be solution! Only a small amount of solution and a large amount of water will have the same effect if you keep them seperated.
The pictures down below explain that to you. Just heat up a big cooking pot of water and seperately prepare some solution. Then put the container with the hot solution in your cooking pot with hot boiling water. Take care that both are closing tightly. If you put your cooking pot in a big box with insulation material, like styrofoam, cotton, rock wool, saw dust etc. you get a real slow cooling down of several days up to over a week. If you use an electronic thermometer you can watch the temperature falling.

Heating up the thermal ballast and your solution seperately	Now the crystals grow in your "cooking box".

Calculating a Solution

You often will have the problem that you need a specific volume of solution to fill a growing vessel efficiently. Lets take for example you want to use the slowly cooling method, have a 1000 ml jar and you want to have about 800 mls of solution which contains 260 gms of sugar per 100 gms of water.
The specific gravity of sugar is 1.587,
so 260 gms have a volume of 260/1.587 = 163.8 ml
+ the 100 gms of water (which are almost exactly 100 mls)
you get a volume of 263.8 mls.
To fill up 800 ml you need 800/263.8= 3.03 times your basic recipe.
That is 3.03*100 gms = 303 gms of water and
3.03*260 gms = 787.8 gms of sugar.
If you take 300 gms of water and 790 gms of sugar you will also be fine.

Conclusion

Following these instruction you did not only learn something about growing sugar crystals but the basics of solution growth anyhow. The principles are the same growing other materials and there are more recipes to come. Please be patient and give me some time. If you have questions or comments or you got nice results please eMail me (pics are welcome).

solubility table for sugar in water

in gms of sugar per 100 gms of water and
ounces of sugar per pound of water

And here the same thing in degrees Fahrenheit !

solubility chart of sugar

Udo J.A. Behner Crystal Growing
Zum Bildchen 62
D-66687 Wadern/Morscholz - Germany
Phone : 06871/91007 - FAX : 06871/91006 eMail : mr.bismuth@t-online.de

© 1998 by Udo J.A. Behner

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