Military Miniatures - Making Molds and Casting
( Originally Published Mid 1950's )
Great moments of dreams and anticipation, some of the longest hours you have ever endured, a rare and exhilarating thrill and satisfying pride all these be yours when you make your first mold and cast your first lead soldier. The mental pictures and plans that fill your mind while you prepare your first mold, the endless hours of waiting for the mold to dry, the thrill that comes when you are ready to pour molten metal into the finished mold, and the pride that surges through you when the casting is pulled from the mold you created with your own hands are not sensations that will dull with repetition. Each time, no matter how often, you create a model and reproduce it in metal in a mold you have made, all these sensations will return.
Mold making and casting is an ancient art that has not changed in principle over the thousands of years since man first learned he could melt metal and pour it into a cavity and produce his tools, ornaments and weapons. Methods have changed and improved until today much of your comforts and pleasures are a result of the mold maker's skill, but with all the refinements in the art, the principle is still to place liquified material into molds and allow it to solidify.
In the early days of casting, when molds were made of stone, the design was cut into the stone and the molten metal poured into the open cavity. Later two piece molds were made of bronze, which naturally produced better and more elaborate castings. It is interesting to note that the lost wax process which is widely used today was well known and used back in the ancient world. No better name could ever be found for this method of casting, because that is exactly what happens in the process — the wax is lost. In lost wax casting the original model is made of wax and then covered with the material that is being used to make the mold. The ancient craftsman usually used clay; today plaster of paris or material of general likeness is used. After the mold is dry, it is placed over heat until the wax is melted and drains out of the mold; molten metal is then poured into the cavity, and when the metal solidifies, the mold is broken away from the casting. Thus, the wax model is lost in the process and the term "lost wax" casting. Although the model and the mold are lost, this method has the advantage of producing beautifully detailed castings which require little if any finishing. This method also allows the casting of undercuts and details that would be impossible to obtain in a two piece mold made of plaster, clay or metal.
You have often wondered no doubt how the fine detail and undercuts were possible in the castings, made by professional military miniature makers, which you purchased from your local hobby shop or miniature figure dealer. These finely detailed castings are possible through the use of vulcanized rubber molds, which are not to be confused with molds made from liquid latex which are used to cast figurines of plaster or other material that does not require heat to liquify. In the vulcanized rubber mold method, a model made of metal is required. This model may be obtained by either the lost wax or plaster of paris method, and extra details can be engraved or soldered to the model before the vulcanized rubber mold is made.
Special equipment is required to make vulcanized rubber molds and although the machinery involved does not cost a fortune, it is far more than the average col-lector would care to invest to cast figures for his personal collection. The vulcanizer or machine in which the molds are made is of necessity a sturdy well-built unit, since a pressure of 15 to 25 tons is exerted in the making of the mold. The rubber used in this method of mold making is cut in discs, two being required for each mold, and it is prepared in various curing textures from soft for models with a great deal of undercut work to hard for thin flat models. The ring that holds the rubber while the mold is being made consists of a sturdy ring and a top and bottom plate all made of steel so they will not collapse under the tremendous pressure exerted to form the mold during the vulcanizing process. One of the rubber discs is placed in the mold ring, and since usually several castings are made at one time in these molds, the metal models are arranged in a circle on the bottom half of the mold rubber. A separator powder is naturally used on the models and between the mold halves to prevent the rubber from sticking to the models and the two halves of the mold from sticking together. The top half of the rubber mold is placed in the steel ring on top of the models and the steel ring plate top is put on; then the whole works is put into the vulcanizer where pressure and heat are applied until the rubber mold is vulcanized.
There is a good reason why rubber molds are made in a disc or round form. Rubber molds are usually used in a centrifugal force casting machine. The pouring point or sprue is in the center of the circle and channels, or a spider, for the molten metal is cut from this sprue to each cavity around the mold. The casting machine spins the mold, while molten metal is being poured into the sprue. This spinning action forces the metal out into the mold cavities under pressure set up by centrifugal force, which accounts for the sharp detail in the finished casting. And since the molds are made of rubber, they are flexible enough that the finished casting, even though it has many undercuts, can be removed without damage to the mold.
There are of course various other methods of casting and there are many small details that have been left out of the foregoing descriptions of casting because of lack of space. The principal reason for the outline of casting methods is so you will better understand what happens when you follow the following instructions in making a mold of your own.
The cost of making a plaster mold in which you can cast metal soldiers is negligible; in fact, most of the items you need are common household items. You will need some wood about a quarter of an inch thick, a good sized cereal bowl or other deep dish, a large spoon, a small round sable or camel hair brush and a larger flat type camel hair brush, a small bottle of linseed oil or any light machine oil, a marble, some string, a common table knife and a sharp model knife or kitchen paring knife, a package of ever plastic clay (the kind that doesn't get hard), and a box of molding powder or plaster of paris.
First make a mold box from the wood, the wood may be thicker than ¼ inch, but shouldn't be thinner than ¼ inch because the moisture of the plaster would warp it. The following sizes may be smaller or larger if you like; however, these measurements make a very practicable size for making military miniature molds. Cut one piece of wood 6¼ inches long and 4 3/4 inches wide; cut another piece of wood ½ inch shorter in both length and width of the first piece, or 5 3/4 inches long and 4¼ inches wide. Cement or nail this piece on top of the first piece you cut, being sure the corners are good and square and the second piece is centered on the first piece. Now cut two pieces of wood 2½ inches wide and 4¼ inches long; two more pieces are then cut 2½ inches wide and 6¼ inches long. These are the sides of your mold box and will fit on top of the edge of the first piece of wood you cut, and around the second piece which you cemented or nailed to the first. Do not fasten the last four pieces of wood you cut, because these are held in place by string while the mold is being made. If you use thicker wood for your mold box, naturally you will have to change the sizes to compensate for the size of step formed where the first and second piece of wood are joined. It is important that all cuts are made good and straight and all corners are square, so your box will be solid when tied together with string.
Now examine your model figure which you are going to use as a pattern for your mold; the important thing is to find the dividing line. The dividing line is the highest line running around your figure between the front and back of your model. If you examine the lower priced lead soldiers, you will find a line of flash (flash is the metal that sometimes leaks out of the sides of a mold when castings are made) which has not been cleaned before painting. This line of flash is the dividing line on the figure. It will also help you to find the dividing line on your model by holding it up to the light, with the light directly to the back of the figure and your eye directly on the front of the figure; the exact line where the light casts a shadow around the figure is the dividing line. When you have decided just where the dividing line is on your model, draw a thin line with ink, or scribe with a sharp instrument. Ink will be better, because it is easier to see and will not mar the model. Always keep in mind that if you do not have the right dividing line, the plaster will hook over your model and you will not be able to remove it from the mold.
The next step in making your mold is to build a cradle for your model out of the plastic clay. On the bottom of your mold box (leave the sides off while you build the cradle) spread about 1/2 inch or so of clay, allow a little to extend over the sides because you can trim that later and make a tight fit when you tie up the sides of the box. Place your model face up on the clay bed you have made; if the model is of sturdy stuff such as metal or wood you can gently press it into the clay until the clay comes al-most to the dividing line you have drawn on the model. Now take bits of clay and build up to the dividing line all around the figure; keep bringing the clay out to the edge of the box so that the figure is in a good firm base and make the clay as smooth as possible. The top of the clay need not be level but should follow the contour of the dividing line right out to the edge of the box. When you have cradled the model to your satisfaction, it is time to use the marble you have been wondering about. In each corner of the clay cradle, as far away from the model as possible, push the marble about half way into the clay making a round indentation. When you pull the marble out, smooth the edges of the clay with your finger; these indentations need not be perfect but must not have an overhang where the plaster can catch under the clay. The indentations will form the keys in the two halves of dividing line is found by holding the model directly in line with the eye. The extreme edge of the silette is where the dividing line should be drawn. The model is then placed in a clay cradle, building the up even with the dividing line.
You are now ready to pour the first half of your mold. Trim the clay that overhangs the sides of the platform on which you built the cradle; be sure to make your cuts as straight as possible, so that when the sides of the mold box are put in place around the platform they will make a tight fit. Now place the two shorter sides you cut in position on each end of the platform and the two longer sides overlapping the short ones. Start with your string at the lower half of the box you have formed and wind it tightly around the box; continue winding the string up the sides of the box until you are satisfied it is good and firm. Take small bits of clay and seal the inside corners of the box, which extend above the cradle holding your model figure. Check the model and the clay cradle to be sure you have done a neat clean job, and you might brush them lightly with the larger camel hair brush to remove any foreign matter that may have accumulated while you were assembling the mold box.
There are almost as many ways of mixing plaster as there are favorite cold remedies; everyone has his own special method and you too will no doubt develop your own special technique after making a few molds. How-ever, if you will follow the instructions given here, you should be able to turn out a satisfactory mold on your first try. In a bowl, place what you judge to be a little more water than necessary to fill your mold box over the clay cradle and model you have prepared. It is much better to have more than you need than to find you have not mixed enough; be generous with your guess on the amount of water needed to fill the space, for you can always throw away what is not needed. Sift the plaster or molding powder through your fingers into the water until dry plaster starts to remain on the surface of the water. Do not drop handfuls of plaster into the water, because it will get lumpy and cause trouble. When you have placed the powder in the water, stir gently and continuously until the mixture starts to thicken, about eight or ten minutes. The longer you stir the mixture, the stronger the mold; however, if the plaster is not poured when it starts to thicken you will risk the danger of its forming a great number of air holes. The plaster is ready to pour into the mold box when it has reached the consistency of heavy cream. As soon as you think the plaster has reached this consistency, tap the side of the bowl sharply several times; this will bring many of the air bubbles to the top and you can quickly scoop them off before pouring the plaster. Now pour the plaster mixture into the mold box and vibrate or agitate the box, for this will cause the air bubbles to come to the surface and escape. Continue this agitation until the plaster begins to become firm and then set the box aside for about an hour until the plaster has become hard.
When you have allowed the plaster in the first half of your mold to harden, remove the sides from your mold box, pick up the plaster, and remove the clay cradle from it. Now lay the plaster, with the model figure still in it, on the bottom of the mold box and apply a coat of oil over the plaster, brushing it in well. You need not put oil on the figure. Place the sides around the plat-form again, tie them tight, seal the inside corners with clay, mix plaster as you did before and pour into the box, agitating it as you did when making the first half of the mold. Again set the box aside for about an hour for the plaster to harden.
Now that the second part of your mold is hard remove the box sides, separate the two halves of the mold, and remove the original model figure. If you have oiled the first half of your mold well, separation will not be a problem. If the sides do not part readily, brush some water on the parting lines and run a dull knife along the line between the two halves; you may tap the knife lightly but with care to avoid chipping the mold. Check the surface and the cavities in the mold halves for pin holes; these are tiny holes that appear when you have not been able to release all the air bubbles through agitation during the pouring of the plaster. Mix a small amount of plaster and with the small brush you will be able to touch up and fill many of these flaws. Do not bother with any holes that do not touch the figure cavity. With your model knife cut the sprue into the plaster; this is usually cut so that the lead will enter either the top or the base of the figure. The sprue is cut like the inside of a cone or funnel; in many cases it is cut into only one half of the mold, but you will have much more success if you will cut it into both halves. The point where the sprue meets the figure cavity must line up on both halves of the mold, but other than this the cuts on the two halves do not need to line up perfectly since the sprue is cut off after the figure is cast. There is no set size for the sprue, but on the average 21/8 inch figure, cut the channel where the sprue enters the figure about 3/16 to ¼ inch across and then taper the channel out to the edge of the plaster mold, at which point it can be up to an inch across. When you pour hot metal into your mold the air must have some place to go, so you will have to cut or scribe very small air channels from various parts of the figure cavity. Air usually builds up at the ends of extended parts such as hands. From the edge of these sections, cut a line out to the edge of the mold; always bring these lines upward (the top of your mold is the end where the sprue is located), never downward, and they must not come near the pouring sprue. These air channels should be no larger than you might scribe with an ice pick; in fact an ice pick makes a very good tool to scribe them. It is also a good idea to bevel all the outside edges of the mold; this will help prevent chipping of the mold when in use. The mold is now ready, but do not pour molten metal into it now. Moisture and molten metal are two things that don't get along well together; your mold must be completely dry before pouring your first metal casting. Drying will take, at the least, a full 24 hours. You may place the mold on a radiator or in the sun to help the drying process. You may even place it in the oven, but avoid heat above 250 degrees in drying the mold.
The mold you have made is what is known as a simple two-piece mold. You are no doubt wondering, what about horses and turned up hats and other things that could not be cast in a two piece mold. In the case of horses, you can cut the horse down the middle and make a set of two piece molds for each half; then assemble the castings. Or you may cut the legs off on either the right or left side of the model and make a two piece mold for the body and two legs; then make another mold for the two legs you have cut off. When the castings are made you can cement or solder the two leg castings onto the body casting you have made. Naturally, there are multiple piece molds; however, in a three-piece mold the insides of the horse's legs would have to be straight in order to remove the mold sections and you would lose the muscle contours on the inside of the horse's legs.
Three-piece molds are easy to make, and here is how you can make one for a figure wearing a turned-up hat. First, draw your dividing lines on your model; these will be around the figure just as they were when you drew them for a two piece mold, except that on the hat you will have two dividing lines which will follow around the edge of the turned-up hat brim. Prepare the clay cradle for your model and bring the cradle up even with the front of the hat; then fill the indentation at the crown of the hat with clay, so plaster will not hook under the model. With your marble make the usual four key indentations in the corners of the mold. Then make a key indentation in the clay directly above the hat, about half way between the model and the edge of the mold. Prepare your plaster, and pour after tying up your mold box sides. When the plaster has hardened for an hour, remove the clay from the mold half. Before pouring the second half, fill in the indentation in the hat top with clay up to the dividing line you have drawn on the back of the hat brim, and bring the clay right out to the edge of the mold in a wedge shape. Make this wedge as heavy as possible for strength, since it will be a pattern for the third piece of your mold. Make a key indentation in the wedge, oil the plaster on the first half of your mold, tie up the sides, pre-pare the plaster, and pour. When the plaster has hardened, separate the two halves you have made and remove the clay wedge extending from the top of the model's hat. Leave the model in the mold halves and oil the section of the halves where you removed the clay. Tie the two halves together with string, set the mold on end with the opening going down to the hat on top, prepare plaster, and pour into this opening, but be sure you fill it to the top of the mold. When the plaster hardens and you separate the parts and remove the model, you will have a three-piece mold. Cut the sprue and air channels the same as you did in the two-piece mold.
The number of pieces you incorporate into a mold is up to your own ingenuity; however, it is better to keep the mold as simple as possible and each section of the mold as heavy as possible, because plaster is fragile and often an ambitious undertaking in a many-pieced mold leads only to confusion for the amateur.
Now after hours of waiting and anticipation you are ready to cast the metal figure. You will need a ladle, some casting metal, a candle, some string, a pair of pliers, and naturally a method of heating the metal. Since lead melts at about 620 degrees Fahrenheit, and most mixtures of metals used for military miniatures melt around this temperature, give or take a few degrees, you can heat your metal on the gas stove or electric burner. If your hobby shop or military miniature dealer cannot supply you with casting metal or a ladle, you might try a hard-ware store or plumber supply house. Metal may also be obtained from dealers in non ferrous metals, which you will no doubt find listed in your telephone directory. Lead makes a very sturdy casting, but it tacks luster and sharp detail; while type metal gives you a bright sharp detailed casting, but is brittle. Just as there are many opinions on cold remedies and mixing plaster, there are many "sworn-by" mixtures of metal for casting, but the general consensus of opinion among amateur figure makers is that a mixture of about 50-50 of lead and type metal gives a sturdy well-detailed casting. The pliers, string and candle you already have — so you are ready to go.
While your metal is heating in the ladle, light your candle and hold it under the cavity of each mold section until the inside of the cavities are good and black; this deposit of carbon is needed only in the cavity of the mold. Various people use different coatings such as stove blackening and graphite; however, there is nothing easier to use or that gives better results than the carbon from a candle. When your mold cavities are coated with carbon, tie the mold together with string and don't forget to use plenty. In fact, there is no need to tie the string if you wrap a lot of it around the mold, since it will have a tendency to bind itself. Naturally, you may use rubber bands; but if the hot metal spills out of the -mold on to the rubber, the lady of the house is promptly going to move your little foundry outdoors. When your metal has melted you will find a scum has formed on the top. You may remove this by scooping it off with a flat stick or piece of metal. One way to test if your metal is hot enough to pour, without a temperature gauge, is to fold a piece of newspaper a few times and quickly dip it into the metal and withdraw it immediately. If the end of the paper is a nice toast brown, the metal is hot enough to pour. Pour the metal steadily into the mold sprue until the metal is even with the top; in just a few moments you will notice a crystallization action of the metal, and when the metal becomes solid at the pouring point, you can unwrap the string, open the mold, and carefully remove the lead casting. The sprue is cut off with the pliers and thrown back into the ladle to be remelted. Now is the time to check if the metal filled all portions of the mold cavity. If it did not, take your model knife and scribe small air channels from the portion of the cavity which did not fill, so that the built-up air may escape when you pour the next casting. If in your eagerness to remove the first casting you broke out a section of your mold and it is in one or several large pieces, you can cement them in place in your mold, but you must allow the cemented section to dry for several hours before you coat the section with carbon and cast another figure.
Remember, plaster molds are not production molds and you can not expect to cast hundreds of figures at one time. If you will give the mold a little rest after several castings, it will last much longer. It is better to have several molds when you are casting and use them in succession; in this manner you will not burn up your molds. One method of making duplicate molds is to place a mold half in the bottom of the mold box and, after oiling it well and tying up the mold box sides, pour plaster into it. This will give you what might be called a positive of the mold half. Repeat the same operation with the other half of the mold. Then when you want to make additional molds, you can cast them from these positives, rather than building a clay cradle around an original figure.
Mold making and casting, like everything creative, requires practice. Each time you make a mold your skill will increase, but no matter how many molds you make, there will always be that thrill of creation that never dies.