Description of a Liquefaction Furnace for Copal and Succin

This is a re-post of a very intriguing coal furnace meant for varnish making but which could easily be used for melting pitch for medieval glue recipes. The simple design of this furnace makes it a fairly easy project for a potter to make one, and has been made and used by modern woodworking purists interested in historic wood varnishes. Note the tapered design of the funnel (it will wedge itself in the hole of the furnace pot) and the metal sieve, which looks a lot like a modern tea sieve. I think some experimentation is in order...

A sample of a similar design (Tingry, 1803):

And a ceramic recreation by a modern potter:

Description of a Liquefaction Furnace for Copal and Succin.
Those who have seen in detail the laboratories devoted to chemistry courses, will form a fairly clear idea of ​​the construction of this furnace, remembering that which serves for the separation of the antimony sulphide from its gangue. But in order to make it serve the object of which we are speaking, we need some correctives, by means of which the liquefaction of the solid resins, and even their mixture with the drying oils, is followed without difficulty.

Figure. Terracotta varnish furnace.

This furnace is shown in fig. 1e. Board 4th. Can be built entirely of terracotta by practicing three large openings in the lower chamber A which replaces the ashtray in the ordinary furnaces. These openings end in a hanger at the base of the upper chamber B or hearth. The arrangement of this base must be such that, in proportion to the curved openings, the pillars which start from the bottom and end in arcades are as small as possible, in order to leave to the Artist all the facilities suitable for the extraction of The liquefied matter, or even for its mixture with the siccative oil, if one always takes this kind of varnish.

The upper chamber B or the hearth of the furnace is separated from the lower part A by a floor or floor which replaces the grating of the ordinary furnaces. This floor has in its middle a circular opening, the diameter of which corresponds to that of a crucible C which it is to receive, and which extends very far into the lower part. This floor can be part of the furnace, or it is removable. In the latter case, it is supported by means of 3 spurs, or by a circular thread projecting into the interior at the level of the hangers. In my furnace this separation is composed of a sheet of sheet covered with a coating of earth with pottery, one inch thick. This last precaution is indispensable in order to remove the heat from the lower part A.

The side walls of this fireplace B are pierced with holes one inch in diameter (2.7 centimeters) and separated from one another by intervals of about 3 inches (8.1 centimeters). These openings are sufficient to fix The development of caloric (heat) to the point suitable for this kind of operation. I write here the proportions of the three parts of this furnace which served in my experiments, and in which I liquefied six ounces of copal in the space of ten minutes, without altering its cost too much.

(M)

---

(M) Overall stove height - - - - - 17 1/4 inches (4,7,3 decim.)
Height of the lower chamber A including the base that is 1 inch thick - - - - - 11 inches (2.9 decim.)
Height of the upper chamber B of the laboratory - - - - - 5 1/2 inches (1.4,3 decim.)
Diameter taken from upper edge and inside of hearth B - - - - - 9 1/2 inches. (2.5.8 decim.)
Diameter of the same piece taken from the floor - - - - - 7 inches. (1.8 decim)

This part has two and a half inches of retreat and it expresses the diameter of the whole lower part of the furnace A.

The shape of the crucible C is very well represented by that of a horn to be played with the dice, the bottom of which would have been suppressed. This crucible has to extend 9 1/2 inches. (2.5.8 decim.)
Its diameter

Superior 4 1/2 inches. (1,2,1,5 decim.)

Lower 2 1/2 inches. (6.3.5 centim.)

The screen D of conical figure has the same diameter as the upper part of the crucible and extends until the birth of the separation floor.

The crucible C is placed in the opening in the middle of the separation floor, so that it rises 3 to 4 inches in the hearth. A point of union with the floor is provided for the fall of ashes or small coals.
Once this arrangement is complete, a kind of screen D (see Figure 2) is placed in the crucible, made of a brass lattice, of a rare (fine?) fabric. This lattice is given the shape of a funnel whose edge is secured around a circle of iron wire or leon bearing the same diameter as the upper part of the crucible C. The retreat experienced by the crucible C in Its form contributes to the stability of this kind of sieve, just as the well-pronounced conical shape of this latter part shelters it from contact with the lateral part of the crucible, an important object for preserving the copal from too great a alteration.
The copal is then placed on this metallic filter in pieces of the size of a small hazelnut, and in various fragments below this size, and the whole is covered with an iron cover E of an inch in thickness, having Care to fill the joint with a soggy earth-leaf to remove any communication with the outside air.

On the other hand, the lower part of the crucible C is filled in water in a shallow saucer F (see FIG. 3) so that it plunges into water from two to three lines ( 6.7 millimeters).

The firebox B is filled with lighted coals up over the iron lid. The first impression of caloric (heat) on the copal is announced by a kind of sparkle resulting from the dilation which reduces it in small splinters. This noise is a precursor very near to liquefaction; it takes place soon after. Then a small palette of iron terminated by a bent tail is insinuated under the cylinder, and it is given the proper motion to precipitate the liquefied portion of the copal under water, and to bring it back into the solid state towards the edges of the saucer . When the operation is finished, the copal is exposed on dry cloths, or on papers with a glue, in order to sprinkle it; It is then piled up and exposed to a gentle heat, to make it lose all its moisture.

During the pouring of the copal, a very delicate portion of oil is separated which remains fluid after the operation. She swims on the water as well as the copal, and gives the latter a bold look. But when the cylinder is sufficiently prolonged, it may be dispensed with making it dive under water, and even to receive matter in water; But a smoke escapes, which may displease the artist. The essential point is to spare the fire so as not to alter the color of the copal. It is recognized that the fire is too lively, when a very thick smoke emits from the lower opening of the crucible; That it is very red, and that the drops falling into the water rise in bladders and make small explosions.

I succeeded in composing the Varnish with oily oil in the same operation, by replacing the water with boiling drying oil, and by maintaining it in this state by means of a mass of hot iron Which served as its support. Mixing of the liquefied material is facilitated by means of a bent spatula; And afterwards the boiling essence is added. One feels the inconvenience of placing under the apparatus itself a volatile and highly inflammable oil.

I will insist more and more sure on the isolated liquefaction of the copal than on the possibility of supplementing its mixture with a drying oil, to make it into a Varnish of the 5th. kind. This new method enables the artist to compose a tréssolide varnish, very little colored, and to dispense with that of copal to drying oil whose composition requires processes which alter the essential qualities of the substance which makes it the base. I can see the time when the artist, freed from all routine prejudices, will confine himself to the use of varnish, of which I here give the formula as cleaner than that of the fifth. To respond to the celerity of the work of printing, and to the views which are proposed, as to the sharpness and solidity of the varnish.

For larger work, the dimensions of this stove may change; But it would be proper to establish the focus properly so called, on a kind of tripod of iron, as shown in Fig. In order to leave the manipulator more comfortable; But I will always insist on the advantage of working only on doses of 4 and 6 ounces (about 183.43 grams) the ease of putting back the material, when the lid joins very well, pronounces on the preference that Small doses should be given over large ones; The copal is less altered. In this case, it is possible to use a metallic cylinder which is joined to cover with the cover. Then the same fire might serve two or three streams.

The precious advantages which are attached to this new method will be felt when the resulting varnishes with gasoline have been tested. The copal thus prepared has different and more extensive properties than those which are given to it by the ordinary method; And it does not have the dark and brown color which it takes at a temperature too high and too prolonged. Plunged here in an atmosphere of caloric (heat), it receives the impression only on the surface which, soon yielding to the power of this agent, escapes, under the liquid state, to the continuation of its action ; New surfaces successively undergo the same effect, and the final result is a copal which is the least altered, and which can not have undergone but a slight modification in the principles of its composition; Between its parts, and which placed so great an obstacle to the solutions sought to be made. Finally, it is possible to compose fatty varnishes with copal, almost without color, using a little colored oil, such as that of carnations, prepared in lead vases, according to the method of Watin.

Similarly, this copal, simply modified, may increase the solidity of the varnishes in alcohol in a more direct manner than when employed in the preliminary preparation. A second liquefaction would give it the property of being more soluble in alcohol; But it would be to be feared that the alteration in its principles, pushed farther, would give it no superiority over the resins most soluble in this liquid. I will finish all that relates to this 4th. Kind of varnish by the exposition of the experiments which I have made by applying our copal, thus prepared, to the most popular vehicles.


Theoretical and practical treatise on the art of making and applying varnishes, Pierre-François Tingry, 1803, 195-202. Translation by Simon St. Laurent.

For the original French text visit:
http://toolbytool.com/resources/fourneau.html

For the original blog post by my friend and translator Simon St. Laurent:
http://toolbytool.com/resources/furnace_English.html

Photo of modern furnace from:
http://www.fullchisel.com/blog/?p=956

Pitch Glue

Pitch glue is mentioned in the 12th century Mappae Clavicula; a little key to Medieval Techniques as an ingredient and has one recipe for a stone glue 122-B which includes pitch.

It is also mentioned in On Divers Arts by Theophilus (ca. 1120 AD):

Chapter 59. The Composition Called Chaser's Pitch
Grind a piece of brick or tile very small and melt some pitch in an earthenware dish and add a little wax. When these are both melted, mix in the powdered tile and stir it vigorously and pour it out into water. When it begins to grow cold, dip both your hands into the water and knead it for a long time until you can stretch the composition and draw it out like a skin. Immediately melt this composition and fill the cruet to the top.

According to MedievalArtisan.info pitch [glue] is used as a firm, grasping, yet flexible material to hold and support a metal sheet.  It can hold the sheet in place and provide a strong surface behind the sheet which gives under pressure - but not too much, or too quickly - for further decoration techniques like Chasing and Repoussé.
http://www.medievalartisan.info/art/Crafts/Metal/MakePitch.aspx

Following are three recipes from modern sources, each with their own interpretations and preferences. Pine pitch glue has been used since antiquity for a variety of gluing chores, including to help attach projectile points and knife blades to a variety of shafts/handles. Especially when combined with sinew, pine pitch glued points, more often than not, break before detaching. But, when a pine pitch glued object is left in really hot sun, it will soften and stick to whatever it touches.


Tree Resin of Pitch Glue
Use tree Resin (sometimes referred to as pitch) from any variety of coniferous species. The clear or yellow resin seeps from anywhere the tree has been injured and often looks like the wood itself. Without binding agents the tree resin would be too brittle, you can use Charcoal, Beeswax, Dry shredded plant matter (typically in the form of animal droppings). A ratio of 2 parts resin to 1 part charcoal/Beeswax/animal droppings works well. Grind the charcoal and animal droppings to a powder - the finer the better so it is worth extra time and effort in the process. In a suitable container, heat the tree resin (be careful while melting because it is flammable) until it become more liquid. Stir the other ingredients until the glue becomes a thick, black, tar-like substance that is very sticky.

The glue mixture will harden very quickly upon removal from the heat source, but will become pliable again as heat is applied. Therefore it is possible to make in advance and store until required for use.

From http://www.ancientcraft.co.uk/Projects/Projects.html


How to make pine pitch glue
-Here’s how to use Pine resin in a homemade glue recipe.
-Collect the resin from a pine tree.  Here’s a method to tap a pine tree to obtain the sap from a tree.
-Melt the resin.  If it ignites, blow out the flame and move the container so the heat is lessened.  Try to not overheat the resin as the compounds are destroyed the longer they are subjected to heat.
-Add 1 part hardwood charcoal powder.  This helps temper the resin and reduces its stickiness.
-Add 1 part filler material.  This can be ground plant material (crushed to a fine powder) or rabbit or deer scat/droppings (dried and ground up).  In a pinch, you may also substitute sawdust, bone dust, or animal hair.  The filler material helps strengthen the glue compound.
-If you wish to make the resultant glue more flexible, so it can be easily worked, add one part fat, tallow, or beeswax to the mixture.
-Mix thoroughly.
-Apply using a stick.

After the glue hardens, it will resembled hardened glass (unless you chose to add beeswax or fat in which case it will be more elastic).

Dried pine pitch glue can be reheated to convert it back to its liquid state.  Dip a stick into the mixture and remove, allowing the glob of glue to harden on the stick.  Re-dip the stick to add additional layers of glue (as it cools, you may wish to roll it between your hands to compress and shape it).  The finished lolly of pine pitch glue can then be carried with you and reheated when needed.

From http://wildernessarena.com/skills/general-repair/how-to-make-pine-pitch-glue


To Make Pine Pitch Glue
Needed: Pine/Fir pitch (sap), Charcoal – finely ground, Plant fibers – coarsely ground (manure).

1. Once you collect enough pine pitch you’ll need to heat it to remove the ‘volatiles’  (turpentine).  You must heat the pine pitch to the point where the turpentine evaporates  away.  Some say to bring the pitch to a low boil for a few minutes and others recommend  just a low simmer for 5-6 minutes.  Both work but the boiling is faster.  Be sure and use a container large enough that it won't boil over or spill.

2.  I filter the hot, liquid pitch through a layer of two of cheese cloth.  Pine pitch, especially if you find large deposits of old pitch, usually contains bugs, moss, twigs and other debris. These can make the glue inferior and much less attractive when you apply it to an arrow or knife.

3.  Make some charcoal and grind it into a fine powder. If you can't make your own charcoal make sure you get chunk charcoal, not the briquettes. Those almost always contain petroleum products and can ruin your glue.

4.  Take the cool charcoal out and grind it into as fine a powder as you can.  I have a great  method - I put two dozen 2 oz lead balls in my tumbler with real small chunks of charcoal and 20 minutes later I have charcoal as fine as can be!

5.  I mix the charcoal into the hot liquid pitch in about a 50/50 ratio or until it starts to feel like soft clay. Some people recommend adding some plant fiber - usually very dry manure (such as elk droppings), coarsely ground between the hands but not finely ground. I do this as well as it seems to give the glue a little more strength.  But I add only about 10%- 20% manure to the pitch/charcoal mixture. You have to mix all three ingredients together at the same time while the pitch is still liquid. It will start to cool and harden fairly quickly.

6.  Most people I know make 'dubbing/daubing' sticks. Take a pencil size stick and coat it with the finished pine pitch glue by rolling one end of the stick around in the glue until you have a glob about the size of a walnut on the stick. You can then use the daubing stick like a stick of ferrule cement, just heat and apply.

7.  You can also store just the clarified pitch by pouring into a small can such as a 6 oz tuna can. To make storing even easier, once the pitch hardens I cut/peel away the can and place the pitch in a plastic Ziploc baggie.  Be sure and store in a cool place.

Last tips - for appearances sake, I always mask off the areas I don't want to get glue on with tape.  And I always have some turpentine on hand for clean-up. Turpentine works the best.

If you do this right, the glue, when applied, will harden like JB-Weld and work great.  If you make a mistake you can re-heat the glue and start over.  Note - do not leave a pine pitch glued object in really hot sun, it will soften and stick to whatever it touches.

From http://www.pugetsoundknappers.com/how_to/pine_pitch_glue.html

How animal glue is made...

In the "Natural History" of Pliny the Elder, book 11 chapter 94, Pliny says that "From the hides of oxen, and that of the bull more especially, glue is extracted by boiling." The entirety of book 16 chapter 83 is on "Woods united with glue."
From http://swingleydev.com/ot/get/237392/thread/


XVIII. Glue made from Hide and Hartshorn
When this has been carefully dried, take some cuttings of the same hide similarly dried and cut them up in small pieces. Take some hartshorn and, with a smith’s hammer, break it up into small pieces on an anvil. Half fill a new pot with them and fill it up with water. Then heat until a third part of the water has evaporated, but taking care not to let it boil. You test it in this way: moisten your fingers in this water, and if, when they are cool, they stick together, the glue is good; but if not, heat it until they do stick together. Then pour this glue into a clean vessel, and again fill the pot with water and heat as before. Do this four times.

Oil of hartshorn is a crude animal oil obtained from the destructive distillation of the deers' bones or horns. https://en.wikipedia.org/wiki/Hartshorn


Theophilus (c.1122) "On Divers Arts" Translated from Latin by C.R. Dodwell to The Various Arts; published by Thomas Nelson and Sons, Ltd. in 1961.

CHAPTER CVIIII HOW GOAT GLUE IS MADE, AND HOW IT IS TEMPERED; AND HOW MANY PURPOSES IT WILL SERVE.
And there is a glue which is known as leaf glue; this is made of clippings of a goat’s muzzles, feet, sinews, and many clippings of skins. This glue is made in March or January, during those strong frosts or winds; and it is boiled with clear water until it is reduced to less than half. Then put it into certain flat dishes, like jelly molds or basins, straining it thoroughly, Let is tand overnight. Then, in the morning, cut it with a knife into slices like bread; put it on a mat to dry in the wind, out of the sunlight; and an ideal glue will result. This glue is used by painters, by saddlers, and by ever so many masters, as I shall show you later on. And it is good glue for wood, and for many things. […]

Cennini, Cennino d’Andrea (lived c. 1360–1427) "Il Libro Dell’Arte" The Craftsman’s Handbook, translated by Daniel V. Thompson, Jr. 1933 Dover Publications, NY (no publishing date, but after 1960).


186. How to make glue from the skin of an ox or a cote.
—Take the skin of an ox or a cow, as thick as you can find it, which has already been tanned for shoes, and put it in a jar and pour water upon it, and make it boil over the fire from daybreak on a summer's day until nearly the third hour of the day, pouring water into it when necessary, or, when it is much diminished, pour off the water, which has boiled so long, and pour in clean water, and make it boil again until the sixth hour. Then pour off this water, which will be  nearly all evaporated, and again pour clean water into the jar over the  same leather, and do  not  renew it  more than once or  twice more. And take great care not  to  let  it  boil over, and then, having boiled it  down to  one-third, pour it  into  a  vase, and  leave it  to cool  all  that  day  and night. In  the  morning of the  next day if  it  is  coagulated in  the  vase, put  your finger upon it.  If  any part of  it  remains sticking to  your finger, you  may know that  it is  not  good, and  may throw it  away as  refuse. Afterwards fill up  the  jar  with water as  before, in  order to  boil it  with the leather ;  and  you must not  fill  it  up  any  more, but  take  all possible care not  to  let  it  boil  over. You will  know when it  is good by  (after you  have boiled it  sufficiently and let  it  cool) putting your finger upon it  as  before, to  see  whether it  is  hard  ; and the  harder you  find  it,  the  better you  may know it  to  be.

Afterwards putting a  small portion of  it  into  an  earthen vase, set  it  on  the  coals and  make it  rather warm. Then, removing the  vase from the  fire, keep it  at  a  moderate heat over a  slow fire  made of  a  few  pieces of  charcoal, lest it  should be  con S.  AUDEMAR DE  COLORIBUS FACIENDIS. 149 grossiores vero quae per  pannum transpire non  poterunt iterum in  ipso  mortario mitte et  molle sicut antea feceras. Et   3emper minutiorem partem per  pannum transpire facias sicut dictum  est  et  repone cum similibus minutiis et  sic  postquam in  mundissi- mum pulverem redegeris stannum protrahe super pergamenum et  super pannum flores et  imagines et  quodcumque opus volu- cris. Et  in  ipso  opera per  loca  que  de  aurare vel  argenteare voles, pones v 

Mrs Merriefield (1849) ORIGINAL TREATISES, DATING FROM THE XIIth TO XVIIIth CENTURIES in the ARTS OF PAINTING William Clowes & Sons. London

Free download at:
https://books.google.com/books?id=2xgGAAAAQAAJ&printsec=frontcover&dq=ORIGINAL+TREATISES,+DATING+FROM+THE+XIIth+TO+XVIIIth+CENTURIES+in+the+ARTS+OF+PAINTING&hl=en&sa=X&ved=0ahUKEwjy28OGucvPAhVCKCYKHTqKDGAQ6AEIHjAA#v=onepage&q=ORIGINAL%20TREATISES%2C%20DATING%20FROM%20THE%20XIIth%20TO%20XVIIIth%20CENTURIES%20in%20the%20ARTS%20OF%20PAINTING&f=false

A neat article on period glue as it pertains to modern wood working:
http://www.oldbrownglue.com/images/articles/Why_not_period_glue.pdf

A class handout with lots of background information on different period glues  :
http://www.rocks4brains.com/glue.pdf