IMPROVEMENTS IN THE CONSTRUCTION OF MOULDS FOR CASTING ALUMINIUM AND OTHER METAL PLATES FOR ARTIFICIAL TEETH; ALSO IN THE METHOD OF CASTING SAID PLATES AND SECURING THE TEETH THEREIN, AND IN APPARATUS CONNECTED THEREWITH, PART OF WHICH IMPROVEMENTS IS APPLICABLE FOR PRODUCING OTHER FINE METAL CASTINGS
Year: 1867

page_text: in the County of Middlesex, for the Invention of "IMPROVEMENTS IN THE
CONSTRUCTION OF MOULDS FOR CASTING ALUMINIUM AND OTHER METAL PLATES
FOR ARTIFICIAL TEETH; ALSO IN THE METHOD OF CASTING SAID PLATES AND
SECURING THE TEETH THEREIN, AND IN APPARATUS CONNECTED THEREWITH,
PART OF WHICH IMPROVEMENTS IS APPLICABLE FOR PRODUCING OTHER FINE
METAL CASTINGS."-A communication from abroad by James Baxter
Bean, of Baltimore, in the State of Maryland, United States of America.
Sealed the 21st January 1868, and dated the 17th August 1867.
PROVISIONAL SPECIFICATION left by the said Alexander Melville Clark
at the Office of the Commissioners of Patents, with his Petition, on
the 17th August 1867.
I, ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of
Middlesex, do hereby declare the nature of the said Invention for "IMPROVE-
MENTS IN THE CONSTRUCTION OF MOULDS FOR CASTING ALUMINIUM AND OTHER
METAL PLATES FOR ARTIFICIAL TEETH; ALSO IN THE METHOD OF CASTING SAID
PLATES AND SECUBING THE TEETH THEREIN, AND IN APPARATUS CONNECTED THEREWITH,
PART OF WHICH IMPROVEMENTS IS APPLICABLE FOR PRODUCING OTHER FINE METAL
CASTINGS," to be as follows:-
The first part of this Invention relates to the construction of moulds for
casting metal plates for artificial teeth.

page_text: In this Invention the contractibility of the aluminium or other metal used
for casting the plates is compensated by the enlargement of the moulds in
which the plates are cast, a new composition being used for the mould,
and a new combination of operations employed in its construction for the
purpose of obtaining the end desired.
The advantages which would result from the use of aluminium plates as a
base for artificial teeth have long been acknowledged by every one acquainted
with the subject, and many efforts have been made to utilize the metal for
this purpose. Although the casting of the metal has long since been attained
in moulds of the dimensions of the patient's mouth yet the plate when cooled
will be so much smaller as to be entirely unfit for the purpose; this difficulty
hitherto deemed insuperable can be entirely overcome by this improved process,
which I shall now proceed to describe in detail. In the first place I take an
impression of the patient's mouth in plaster of Paris, either in a thin elastic
impression cup or in the usual way, I deem the thin elastic impression cup far
preferable for the purpose, and I use one of thin sheet brass struck up between
dies so as to make an approximate fit to the patient's mouth. This cup or
plate is coated on its upper surface with a thin coating of gum shellac. While
warmed over a lamp to the melting point of the shellac the whole is quickly
enveloped in a handful of cotton which is pressed upon it until cool, when the
superfluous cotton is removed, thus leaving a coating of adherent fibre which
will effectually retain the thin film of plaster used for the impression, which is
now taken in the usual manner, using however much less plaster than by
the ordinary impression cup. The elasticity of this cup allows the plaster to
expand freely, and moreover it is easily removed from the impression cup
when desired by heating it to the melting point of the shellac.
Secondly. Into this impression just taken after being varnished as usual
- east a model of plaster of Paris.
Thirdly. Upon this model after being varnished I form a mould composed
of the best calcined plaster of Paris. The mould is made in several pieces,
..say six in number, three of which form the sides or walls and the other three
the bottom of the mould, each fitting into the other by short dowels or pro-
jections and recesses on their contiguous surfaces. The pieces thus fitted may
be held together by a band of india-rubber or any other suitable fastening.
Fourthly. In this mould after being varnished I cast a compound of two
parts by weight of powdered pumice stone and one part of plaster of Paris
mixed with water; I first boil the powdered pumice in water for a moment
to expel the air, then wash and cool, and afterwards add the plaster. The
composition having become solid the parts of the mould are removed very

page_text: carefully, one at a time, to prevent injury to the fragile cast. This cast is the
matrix on which the perfect fitting plate is produced, and forms a part of the
mould in which the aluminium is to be cast.
The object to be attained by the foregoing operations is accomplished in
the following manner :-From careful experiments and delicate measurements
I have found that; after allowing for the expansion of the impression first cast,
plaster, mould, and matrix, and for the contraction of the mould and aluminium.
or other metal a plate will be produced two-thousandths of an inch larger than
the gums from which the impression was taken which is necessary for a
comfortable fit, and adheres more perfectly to the gums by atmospheric
pressure than any other heretofore produced. In order to complete the
mould for casting the plate for a set of teeth the model or pattern plate of
wax, or wax and tin foil, is prepared as if for a cast of vulcanite work, except
that the plate is one half the thickness usually employed for vulcanite; the
teeth or blocks having their pins embedded in plaster and trimmed smooth so
as to form the groove in the plate along the line of the teeth for the purpose
of fastening the teeth thereto and also to enable them to be easily separated
from the wax. The teeth or blocks are now oiled all over their surface and
placed in their proper place on the wax model in the articulator, if necessary,
and hot melted wax is introduced under and around each tooth and block, so
as to fill up all the vacancies between and beneath the teeth or blocks; the
wax is also carefully modelled to represent all the fullness and outlines desired
in the aluminium plate. The plate and teeth are now placed upon the matrix
and the edges secured all round by melted wax, and the whole made as
smooth as possible; the teeth are now carefully removed from the wax plate
so that none of the wax comes away with them. The groove into which
the pins of the teeth or blocks project is now cut out all along the line of the
teeth, which are again replaced and any damage to the wax fitting against
them repaired. This matrix containing the pattern plate and teeth is now
secured in the lower half of the flask by means of the composition of two
parts of pumicestone and one of plaster mixed with water in the same
manner as if for a case of vulcanite work; the teeth are now removed and the
whole surface of the wax and composition is oiled. The upper portion of the
flask is then put on and fitted in like manner, making provision for the gate
and vents; when solid the flask is warmed, opened, and the wax pattern plate
removed leaving the desired mould for the aluminium plate.
The second part of the Invention relates to the casting of aluminium or
other metal plates in fine moulds. The metal is cast in fire moulds under
pressure of a high column of the metal itself contained in a conduit of scap:.

page_text: stone, earthenware, or other similar substance heated to about the melting
point of the metal cast. The moulds and conduit at the moment of casting
are filled with hydrogen or other gas which does not contain oxygen. In
casting aluminium and several other metals possessing similar properties,
the great difficulty has hitherto been the impossibility of producing a solid
casting having all the details of a fire-mould faithfully represented. The
source of this difficulty is mainly owing to the extreme lightness of the metal,
and the tough film of oxide which forms on the surface of the melted mass as
soon as it comes in contact with the air. These two properties combine to
prevent the melted metal from flowing into the more minute details and parts
of the mould, and at the same time prevent the closing up of faults and air
cells in the body of the casting. Aluminium, especially in its pure state, is so
very light and the film of oxide is formed so thick and tough the moment it
comes in contact with the oxygen of the air as to render it practically worthless
for casting by the old methods. Still another difficulty in casting any metal,
but particularly in casting alumimiun, arises from its great contractibility in
cooling, by which holes and imperfections in the surface of the casting occur,
rendering it indispensable to success that means should be devised for
counteracting the effect. I propose to obviate all these difficulties by a process
which renders the casting of aluminium and other metals of kindred properties
in fire-moulds for the purposes of the dentist, the jeweller, the artist, or others
who have to make fine metal castings as easy and uniformly successful as
has been the casting of gold and silver heretofore. I provide a stand with a
heavy base having four posts projecting upwards from it, two of the posts
having set screws passing through them. This device serves for holding the
flask containing the mould firmly in an upright position and at the same time
for binding together the two halves of the mould. The outside flask is com-
posed of two similar parts, one baving two or three projections fitting into
corresponding recesses or between pins in the other to indicate the proper
relative position of the two parts of the flask. The two sides of the flask
contain a number of holes for the purpose of giving vent to steam and gases
that may
accumulate in the interior of the mould. One side is made movable
for the purpose of filling in the last portions of the composition forming the
mould. Two projections are also made on either side of the gate or mouth of
the flask for the reception of vents, which vents communicate with the interior
cavity of the mould at two of its highest points and permit of the escape of
the æriform or gaseous contents of the mould as the metal fills it. I fill the
outer portion of these vents with small metallic rods or wires, between which
the air will escape readily and yet prevent the escape of the metal by cooling

page_text: it so rapidly as to congeal it by the time it has advanced half an inch or more
among the rods; the flask thus formed contains within it a mould or matrix
of the article to be cast as before-mentioned. I make this mould of a compound
of about two parts by weight of powdered pumicestone and one part of fine
calcined plaster of Paris mixed together with water to the consistency of cream
or thin batter, and poured over the model of the article to be cast in the manner
usually practised in making such moulds in plaster of Paris. The 'melted
metal is introduced into the mould through a long tube or conduit composed
of soapstone, earthenware, or other substances equally capable of enduring the
necessary heat and not liable to contaminate the metal with impurities. This
conduit is made in two parts, the lower one being fastened to the flask and
the upper one, which should be at least ten inches in length for aluminium, is
made detachable for the purpose of being heated separately, and also for the
purpose of emptying it of the melted metal contained after that in the mould
has become solid; the two parts are fitted together by a ground joint. The
whole apparatus being thus constructed it remains to show the method of
operation. In the first place I expose the mould or matrix together with the
flask to a gentle heat until it is completely dried and heated to from three
hundred to four hundred degrees Fahrenheit and the point of the gate is heated
to redness; at the same the upper portion of the conduit is uniformly
heated to a point at or above the melting point of the metal to be used, and
the metal itself in sufficient quantity to fill the mould and conduit is heated to
a degree somewhat above its melting point. The flask containing the mould
in its heated state is now placed in the stand or holder and the set screws
tightened to a proper degree. The vents containing their bundles of wires or
rods are now placed while cold in their places on each side of the gate, and
the upper portion of the conduit heated as above-described is put in place and
attached by means of the ground joint. I next fill the whole apparatus with
common illuminating gas, hydrogen, or other gas entirely free from oxygen,
by means of a pipe leading from the source of supply of the gas and passing
through a small plate or disc of mica placed on the open end of the conduit,
the gas forced into the mould issuing at the vent until all is completely
filled. The gas pipe and plate of mica are now quickly removed and the
molten metal poured in without delay, so as to fill up the mould and conduit
to the top. As soon as the metal in the mould has become solid, and before
it has congealed in the conduit, I detach the upper part and let the melted
metal run out, for if it is allowed to become solid in the conduit this portion
of the apparatus might be destroyed in removing it therefrom or in subsequent
manipulations of the flask. In this manner a solid and perfect casting can he

page_text: made from the lightest and most easily oxydizable metals. The air being pre-
vented from coming in contact with the metal in the mould there will not
be any oxide formed on its surface, and under pressure of the high column of
fluid metal it flows rapidly and easily into all the finest parts of a delicate
mould and brings out all the details of the design. As the metal cools and
contracts in the mould by the pressure of the superheated molten metal in the
conduit it flows in and supplies the deficiency until the casting is complete,
thus absolutely remedying all the evils of its great expansibility by heat. The
pressure of the column of metal may be regulated at pleasure by making the
conduit of a height proportionate to the specific gravity of the metal to be
cast. Silver, gold, and other heavy metals may be cast by means of this
apparatus with much greater perfection than by the old methods.
The whole apparatus is simple and easily worked, and if the process
described be followed is uniformly successful in producing most perfect castings,
however delicate may be the moulds.
above-
The third part of this Invention relates to securing artificial teeth to such
cast plates. A cast of aluminium or other similar metal is employed having
recesses into which the teeth are fitted; a groove is left behind the teeth-
between them and the plate, into which the pins attached to the teeth project
when in place; this groove having pits or recesses along its sides is after-
wards filled with melted tin under pressure, the teeth being thus firmly
'secured to the plate. This plate is prepared and the fastening of the teeth
is effected in the following manner :-
First, I cast a plate of aluminium or other metal in the manner before
described having around the line which the teeth are to cover a recess or
cavity; the lower edge of this recess terminates in a deep groove in which
the necks of the teeth or thin edges of the artificial gums are stepped and
confined securely, being fitted close against the plate on all sides. A groove
. at the upper part of the recess along the line extends all round the plate
: between it and the teeth into which the platinum pins of the teeth or blocks
project; this groove has along its sides pits, holes, and recesses cut or drilled
into the thicker portions of the plate, and also all rough and jagged points or
undercuts that can be obtained; this groove is made so deep that when the
teeth are all fitted to the plate the cavity along this line is not filled up, but
an empty chanuel remains behind the teeth running along the line of the
platinum pins the whole length of the line of teeth. When the plate has been
• constructed in this shape the teeth are inserted in their proper places in the
. recess, and secured by running a little melted wax along the line of junction
of the teeth with the plate, completely stopping up all crevices between and

page_text: around the teeth leading toward the groove behind the teeth. Two small
cylinders of wax close the two exits of the channel and project a short distance
above the teeth. The whole is now ready to be placed in the investment of
pumice stone and plaster for the permanent fastening of the teeth to the plate.
This is effected in the following manner :-First, I provide myself with a
flask of suitable form; this flask I fill about one-third full of a composition
of two parts by weight of powdered pumice stone and one part of calcined
plaster of Paris mixed with water and allowed to harden. The plate having
the teeth fixed to it as described is then placed upon the layer of composition
in the flask, the teeth projecting upward, and another similar portion of the
same composition poured in sufficient to completely envelop the plate and
teeth and leave the two small cylinders of wax projecting above; this layer
of composition becoming hardened the wax cylinders projecting above it are
melted down even with the surface by means of a hot instrument. Two stout
brass tubes of a funnel form are placed with their small ends downward, one
over each of the wax cylinders, and being warmed they embed themselves in
the wax.
A third portion of the composition above described is now poured
in filling up the flask to near the top of the brass tubes. Two high conduits
of cast iron or other suitable material, about five inches in length, are made
to fit into the conical cavities of the brass tubes fixed into the flask, by means
of a close fitting ground joint but so as to be easily put in or removed. The
flask is now dried by a gentle heat and heated to about the melting point of
tin. The wax being melted is entirely absorbed from around the teeth by the
surrounding composition. The wax cylinders likewise disappear and an open
channel now remains running from the bottom of one brass tube around at
back of the teeth connecting with all the minute interstices between and
behind the teeth to the bottom of the other brass tube over the other extremity
of the plate. The brass tubes are now exposed to the heat so as to be soine-
what above the temperature of the remainder of the flask, and the conduits
are heated almost to redness and dropped into their places in the brass tubes.
Pure tin heated to about the temperature at which olive oil takes fire is now
poured into one of the conduits; the metal thus poured into the conduit flows
down through the empty channel and up into the other conduit. The first
conduit.is kept full, and as soon as the metal appears' in the second it also is
filled to the top by pouring the metal into it. As soon as both conduits are
full a wet cloth is applied to the outside of the flask so as to cool its contents,
first, while the pressure is kept up by the fluid metal in the conduits. If the
metal in the conduits were first cooled that in the groove behind the teeth
would all be drawn out to supply the deficiency caused by the shrinking;

page_text: while by cooling the groove first the first shrinking takes place in the conduits,
and the metal will be found to have been forced into every minute pore and
crevice between and around the teeth and platinum pins, and into the pits,
undercuts, and retaining points along the channel, thereby most effectually
securing the teeth to the plate. As soon as the whole apparatus has suf-
ficiently cooled the composition is carefully removed from around the teeth,
the plate with the conduits attached removed from the flask, and the gates
cut off at the bottom of the brass tubes. The brass tubes can now be
removed from the conduits and the metal melted out of the latter. The teeth
thus fastened to the plate are attached as perfectly as if they were a part of
the metallic plate itself, and the work is more easily repaired than any other
kind in use. Should the teeth become injured or broken they may be
removed from the plate, and by supplying the broken portion with a new block
from the same mould, and repeating the operation above described, it is rendered
as perfect as before the injury. The same process can also be used for
securing the teeth to lower sets cast in solid gold or silver, thereby securing
weight in a lower set, which is as great a desideratum as lightness in an
upper set.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Alexander Melville Clark in the Great Seal Patent Office
on the 15th February 1868.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ALEXANDER
MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Seventeenth day of August, in the year of our Lord
One thousand eight hundred and sixty-seven, in the thirty-first year of Her
reign, did for Herself, Her heirs and successors, give and grant unto me, the
said Alexander Melville Clark, Her special licence that I, the said Alexander
Melville Clark, my executors, administrators, and assigns, or such others
as I, the said Alexander Melville Clark, my executors, administrators, and
assigns, should at any time agree with, and no others, from time to time and at
all times thereafter during the term therein expressed, should and lawfully
might make, use, exercise, and vend, within the United Kingdom of Great
Britain and Ireland, the Channel Islands, and Isle of Man, an Invention for
"IMPROVEMENTS IN THE CONSTRUCTION OF MOULDS FOR CASTING ALUMINIUM AND

page_text: OTHER METAL PLATES FOR ARTIFICIAL TEETH; ALSO IN THE METHOD OF CASTING
SAID PLATES AND SECURING THE TEETH THEREIN, AND IN APPARATUS CONNECTED
THEREWITH, PART OF WHICH IMPROVEMENTS IS APPLICABLE FOR PRODUCING OTHER
FINE METAL CASTINGS," a communication to me from abroad by James'
Baxter Bean, of Baltimore, in the State of Maryland, United States of
America, upon the condition (amongst others) that I, the said Alexander
Melville Clark, my executors or administrators, by an instrument in writing.
under my, or their, or one of their hands and seals, should particularly.
describe and ascertain the nature of the said Invention, and in what manner
the same was to be performed, and cause the same to be filed in the Great,
Seal Patent Office within six calendar months next and immediately after.
the date of the said Letters Patent.
NOW KNOW YE, that I, the said Alexander Melville Clark, do hereby
declare the nature of the said Invention, and in what manner the same is
to be performed, to be particularly described and ascertained in and by the
following statement, reference being had to the Sheet of Drawings hereunto
annexed and to the letters and figures marked thereon (that is to say) :-
The first part of this Invention relates to the construction of moulds for
casting aluminium and other metal plates for artificial teeth.
According to this Invention the contractibility of the aluminium or other
metal used for casting the plates is compensated by the enlargement of the
moulds in which the plates are cast, a new composition being used for the
mould, and a new combination of operations employed in its construction for
the purpose of obtaining the end desired. The advantage which would result
from the use of aluminium plates as a base for artificial teeth have long been
acknowledged by every one acquainted with the subject, and many efforts
have been made to utilize the metal for this purpose. Although the casting
of the metal for this purpose has long since been attained in moulds of the
dimensions of the patient's mouth yet the plate when cooled will be so much
smaller as to be entirely unfit for the purpose; this difficulty bitherto deemed
insuperable can be entirely overcome by the new process of this Invention
and which I shall now proceed to describe in detail, reference being had' to
the accompanying Drawings.
Figure 1 represents a top view of the impression cup C; Figure 2 shows
the upper side of the mould D; Figure 3 is a top view of the mould B;
Figure 4 is a bottom view of the same; and Figure 5 is a view of the
concave side of the matrix.
In the first place I take an impression of the patient's mouth in plaster of
Paris, either in a thin elastic metallic impression cup or in the usual way, I
'

page_text: deem the thin elastic metallic impression cup C as far preferable for the
purpose, and I use one of thin sheet brass struck up between dies so as to
make an approximate fit to the patient's mouth; this cup or plate is coated
on its upper surface with a thin coating of gum shellac. While warmed over a
lamp or otherwise to the melting point of the shellac the whole is quickly
enveloped in a handful of cotton which is pressed upon it until cool when the
superfluous cotton is removed, thus leaving a coating of adherent fibre which
will effectually retain the thin film of plaster used for the impression which is
now taken in the usual manner, using however much less plaster than by the
ordinary impression cup. The elasticity of the cup allows the plaster to
expand freely, and moreover is easily removed from the impression when
desired, by heating it to the melting point of the shellac.
Secondly, into this impression just taken after being varnished or otherwise
prepared as usual I cast a model D of plaster of Paris.
Thirdly, upon this model after being varnished or otherwise prepared I
form a mould B in several parts composed of the best calcined plaster of
Paris. The Drawings show a mould for making a set of artificial teeth,
which give perfect satisfaction, in which six pieces are used, three b, ¹, b³,
forming the sides or walls, and three 63, 64, 65, forming the bottom of the
mould all being of the shape shown in Figure 4, and each fitting into the
other by short dowels or projections and recesses on their contiguous surfaces.
The pieces thus fitted to each other may be held together by a band of india-
rubber or any other suitable fastening.
Fourthly, into this mould after being varnished I cast a compound of two parts
by weight of powdered pumice stone, and one part of plaster of Paris mixed with
water. I first boil the powdered pumice stone in water for a moment to expel
the air, then wash and cool and afterwards add the plaster. The composition
having become solid the parts of the mould are removed carefully one at a
time to prevent injury to the fragile cast. This cast is the matrix on
which the perfect fitting plate is produced, and forms a part of the mould in
which the aluminium is to be cast.
The object to be attained by the foregoing operations is accomplished in
the following manner :-From careful experiments and delicate micrometer
measurements it is found that a cast aluminium plate two and a half inches
in width on being heated from the ordinary temperature of the mouth to near
the melting point of the metal expands of an inch. An impression in
plaster of an equal width, in a thin elastic impression cup, expands in
setting in the same distance. A plaster model cast into this
impression expands 1000; the mould formed on this model expands 10.800.
250

page_text: 60
The contraction of the aluminium plate may be put down at 16.8% in
cooling from its point of congelation to the temperature of the mouth. Then
the contraction of the mould in drying may be safely put down' at 10.000, then
0260+00160276 the whole sum of contractions 0296-0276=10020.
This gives a plate two one-thousandths of an inch larger than the gums
from which the impression was taken, which is necessary to a comfortable fit;
these measurements determined before the actual experiment with a dental
plate was tried are found to work out exactly in practice, and the result is a
most perfect fitting plate adhering more perfectly to the gums by atmospheric
pressure than any other heretofore produced.
other heretofore produced. In order to complete the mould
for casting the plate for a set of teeth the model or pattern plate of wax or
wax and tin foil is got up as if for a cast of vulcanite work, except the plate
is one-half the thickness usually employed for vulcanite. The teeth or blocks
have their pins embedded in plaster and trimmed smooth, so as to form the
groove in the plate along the line of the teeth, for the purpose of fastening
the teeth thereto, and also to enable them to be easily separated from the
The teeth or blocks are now oiled all over their surface and put in
their proper place on the wax model, in the articulator if necessary, and hot
melted wax is introduced under and around each tooth and block, so as to
fill up all the vacancies between and beneath the teeth and blocks; the wax
is also carefully modelled to represent all the fulness and outlines desired in
the aluminium plate. The plate and teeth are now placed upon the teeth
and matrix, and the edges secured all round by melted wax, and the whole
made as smooth as possible. The teeth are now carefully removed from the
wax plate, being careful that no wax comes away with them; now cut out
the groove into which the pins of the teeth or blocks project all along the
line of the teeth, again replace the teeth, and repair any damage to the wax
fitting against them. This matrix containing the pattern plate and teeth. is
now secured in the lower half of the flask by means of the composition of two
parts of pumice stone and one of plaster mixed with water in the same manner

page_text: as if for a case of vulcanite work. The teeth are now removed and the
whole surface of the wax and composition is oiled. The upper portion of the
flask is then put on and filled in like manner, making provision for the gate
and vents. When solid the flask is warmed, opened, and the wax pattern
plate removed, leaving the desired mould for the aluminium plate.
What I claim as new and desire to secure by Letters Patent under the
first head of this Invention is,-
1st. The thin metallic impression cup C for the purpose specified.
2ndly. I claim the use of the model B made in several pieces substantially
as and for the purpose described.
3rdly. I claim the process of constructing moulds for casting aluminium
plates for artificial teeth, substantially as above described.
The second part of this Invention relates to the casting of aluminium or
other metal plates in fire moulds; the metal is cast into fire moulds under a
pressure of a high column of the metal itself contained in a conduit of soap-
stone, earthenware, or other similar substance heated to about the melting
point of the metal cast. The moulds and conduit at the moment of casting
are filled with hydrogen or other gas containing no oxygen. In casting
aluminium and several other metals possessing similar properties the
great difficulty has hitherto been the impossibility of producing a solid casting
having all the details of a fire-mould faithfully represented. The source of
this difficulty is mainly from the extreme lightness of the metal and the
tough film of oxide which forms on the surface of the melted mass so soon
as it comes in contact with the air; these two properties combine to prevent
the melted metal from flowing into the more minute details and parts of the
mould, and at same time prevent the closing up of faults and air cells in
the body of the casting. Aluminium especially in its pure state is so very
light, and the film of oxide is formed so thick and tough the moment it comes
in contact with the oxygen of the air, as to render it practically worthless for
casting by the old methods; still another trouble in casting any metal, but
particularly annoying in casting aluminium arises from its great contractibility
in cooling, by which holes and imperfections in the surface of the casting
occur, rendering it indispensable to success that means should be devised for
counteracting this effect.
In the Invention to be hereafter described I propose to obviate all these
difficulties by a process which I have been testing and perfecting for years,
and which I am able at last to say renders the casting of aluminium and
other metals of kindred properties in fire moulds for the purposes of the

page_text: dentist, the jeweller, the artist, or any others who have to make fine. metallic
castings as easy and uniformly successful as has been the casting of. gold and
silver heretofore.
A, A, Figures 6 and 7 of the Drawings, represent a side elevation and
plan of a stand with a heavy base, having four posts a, a, a, a, projecting
upward from it, two of the posts having set screws a', a¹, passing through
them. This device is for the purpose of holding the flask containing the
mould firmly in an upright position, and at the same time binding together
the two halves of the mould. B, B, represents the flask which I fix in the
stand A, as shown in the Drawings. The outside flask is composed of two
similar parts B and B', one having two or three projections b, b, b, fitting into
corresponding recesses, or between pins 61, 61, 61, in the other, to indicate the
proper relative position of the parts B and B to each other. The two sides
B and B contain a number of holes c, c, c, c, for the purpose of giving vent to
steam and gases that may accumulate in the interior of the mould. One of
the sides B³ is movable for the purpose of filling in the last portions of the
composition forming the mould. The projections d², d, on either side of the
gate d, are pierced for the reception of the vents C, C. The flask thus formed
contains within it a mould or matrix of the article to be cast. I make this
mould of a compound of about two parts by weight of powdered pumice
stone and one part of fine calcined plaster of Paris, mixed together with water
to the consistency of cream or thin batter, and poured over the mould of the
article to be cast, in the manner usually practiced in making such moulds in
plaster of Paris. Vents C, C, are placed on either side of the gate d, and
communicating with the interior cavity of the mould at two of its highest
points; these permit the escape of the aeriform or gaseous contents of the
mould as the metal fills it. I fill the outer portion of these 'vents in the
manner shown in the Drawing with small metallic rods or wires e, e, e,
between which the air will escape readily, and which will yet prevent the
escape of the melted metal by cooling it so rapidly as to congeal it by the
time it has advanced half an inch or more among the rods. The melted metal
is introduced to the mould through the high conduit D, composed of soap-
stone, earthenware, or other substance equally capable of enduring the
necessary heat, and not liable to contaminate the metal with impurities. The
conduit D is made in two parts, the lower d is fastened into the flask B, B',
as shown in the Drawings, and the upper d', which should be at least ten
inches in length for aluminium, and is made detachable for the purpose of
being heated separately, and also for the purpose of emptying it of the melted

page_text: metal contained in it after that in the mould has become solid. The two
parts are fitted together by the ground joint dr.
The whole apparatus being thus constructed it remains to show the method
of separating it.
In the first place I expose the mould or matrix together with the flask
B, B, to a gentle heat until it is completely dried and is heated to about
300 or 400 degrees Fahrenheit, and the point of the gate d is heated to
redness. At the same time the upper portion d of the conduit D is uniformly
heated to a point at or above the melting point of the metal to be used,
and the metal itself in sufficient quantity to fill the mould and conduit is
heated to a degree somewhat above its melting point. The flask containing
the mould in its heated state is now placed in the stand or holder A, as shown
in Figures 6 and 7, and the set screws tightened to a proper degree. The
vents C, C, containing their bundles of little rods e, e, are now put while cold
into their places on each side of the gate d, and the upper portion of the
conduit heated as above described is put in place, and attached by means of
the ground joint d³. I next fill the whole apparatus with common illuminating
gas, bydrogen, or other gas entirely free from oxygen, by means of a pipe
leading from the source of supply of the gas, and passing through a small
plate or disc of mica placed on the open end of the conduit, and the gas
forced into the mould issuing at the vents until all is completely filled. The gas
pipe and plate of mica are now quickly removed, and the molten metal
poured in without delay, quickly filling up the mould and conduit to the top.
As soon as the metal has become solid in the mould, and before it has con-
gealed in the conduit D, I detach the upper part d' and let the melted metal
run out, for if allowed to become solid in the conduit this portion of the
apparatus might be destroyed in removing it therefrom, or in subsequent
manipulations of the flask. In this manner a solid and perfect casting can
be made from the lightest and most easily oxidized metals. The air being
unable to come in contact with the metal in the mould no oxide is formed on
its surface, and under pressure of the high volume of fluid metal it flows
rapidly and easily into all the finest parts of a delicate mould, and brings out
all the details of the design. As the metal cools and contracts in the mould
by the pressure of the superheated molten metal in the conduits it flows in and
supplies the deficiency until the casting is complete, thus absolutely remedying
all the evils of its great expansibility by heat. The pressure of the column of
metal may be regulated at pleasure by making the conduit of a height pro-
portionate to the specific gravity of the metal to be cast. Even silver and

page_text: gold and heavy metals are cast by means of this apparatus with much
greater perfection than by the old methods. The whole apparatus is simple
and easily worked, and if the process above described be followed is uniformly
successful in producing most perfect castings, however delicate may be the
moulds.
What I claim as new, and desire to secure by Letters Patent under the
second head of this. Invention is,-
1st. The frame or holder A having the posts a, a, a, a, and the set screws
a', a', constructed as described.
2ndly. The flask B, B', having the vents C, C, and the gate d, substantially
as described.
3rdly. The method above described of stopping the vents C, C, with the
small rods e, e, e..
4thly. The conduit D composed of soapstone or other similar material, and
formed in two parts d, d', as and for the purpose described.
5thly. The compound above described of which the mould or matrix is
formed.
P
6thly. The method above described of casting alnminium and other similar
metals in fire moulds, substantially as described.
7thly. The casting of aluminium or other easily oxidized metals into moulds
filled with gases destitute of oxygen, as and for the purpose described.
The third part of this Invention relates to the mode of securing artificial
teeth to cast plates.
Figure 8 represents a perspective view of this Invention, a portion of the
flask being removed to show the interior construction and arrangement of the
apparatus; Figure 9 is a perspective view of the plate with the teeth attached ;
Figure 10 is a vertical cross section of the plate and one of the teeth attached
to it.
In this Invention a plate cast of aluminium or other similar metal is
employed, having recesses into which the teeth are fitted.
A groove is left
behind the teeth between them and the plate, into which the pins attached
to the teeth project when in place. This groove having pits or recesses along
its sides is afterwards filled with melted tin under pressure, the teeth being
thus firmly secured to the plate.
In the Drawings D, Figure 9, represents the plate upon which the teeth ḍ, d,
are to be fixed. This plate is prepared and the fastening of the teeth effected
in the following manner :-First, I cast a plate of aluminium having around
the line which the teeth are to cover a recess or cavity E, E.. This plate with
four teeth removed to exhibit clearly the construction is shown in Figure 9 of

page_text: the Drawings. It will be observed that the lower edge of this recess termi-
nates in a deep sharp groove e, in which the necks of the teeth or thin edges
of the artificial gums d, d, are stepped and confined securely, being fitted
close against the plate on all sides. It will also be observed that a groove e¹, e¹,
at the upper part of the recess E, E, along the line e, es, extends all around
the plate between it and the teeth, into which the platinum pins of the teeth
blocks project. This groove has along its sides pits, holes, and recesses cut
or drilled into the thicker portions of the plate, and also all rough or jagged
points or undercuts that can be obtained. And I would now say that the
strongest and most reliable of these pits and holes are obtained by drilling
through septums of the aluminium cast upon the plate along the groove or
channel before mentioned, so as to come between the blocks or pins, which
septums at first form barriers along this groove, but by drilling or tunneling
through them a continuous channel is formed, into which the pure tin or a
suitable alloy, say of tin, silver, and calcium, is afterwards injected, so as to
completely interlock the platinum pins of the teeth with the plate itself; this
groove is made so deep that when the teeth are all fitted to the plate the
cavity along this line is not filled up, but an empty. channel remains behind
the teeth running along the line of the platinum pins the whole length of the
line of teeth from the point i to the point ¹. When the plate D has been
constructed in this shape the teeth d, d, are inserted in their proper places in
the recesses E, E, and secured by running a little melted wax along the line
of junction of the teeth with the plates, completely stopping up all crevices
between and around the teeth leading toward the groove e¹, e', behind the
teeth. Two small cylinders of wax g, g, close the two exits of the channel, ¹,
and project a short distance above the teeth. The whole is now ready to be
placed in the investment of pumice stone and plaster for the permanent
fastening of the teeth to the plate. This is effected in the following manner :-
First, I provide myself with a flask A of the form shown in the Drawing,
Figure 8. This flask I fill about one-third full of a composition of two parts
by weight of powdered pumice stone and one part of calcined plaster of Paris
mixed with water and suffered to harden. The plate D having the teeth fixed
to it as above described is then placed upon the layer of composition in the flask,
the teeth projecting upward and another similar portion of the same compo-
sition poured in, sufficient to completely envelop the plate and teeth and leave
the two little cylinders of wax g, g, projecting above. This layer of composi-
tion becoming hardened the wax cylinders projecting above it are melted
down even with the surface by means of a hot instrument. Two stout brass
tubes B, B, of a funnel form are placed with their small ends downward, one

page_text: over each of the wax cylinders g, g, and being warmed they embed themselves
in the wax. A third portion of the composition above described is now poured
in, filling up the flask to near the top of the brass tubes. The two high
conduits C, C, of cast iron or other suitable material above five inches in
length are made to fit into the conical cavities of the brass tubes fixed into the
flask by means of a close fitting ground joint, but so as to be easily put in or
removed. The flask is now dried by a gentle heat and heated to about the
melting point of the tin. The wax being melted is entirely absorbed from around
the teeth by the surrounding composition. The wax cylinders g, g, likewise
disappear and an open channel now remains running from the bottom of one
tube B around back of the teeth, connecting with all the minute interstices
between and behind the teeth to the bottom of the tube B over the other
extremity of the plate. The brass tubes B, B, are now exposed to the heat,
so as to be somewhat above the temperature of the remainder of the flask, and
the conduits C, C, are heated almost to redness and dropped in their places
B, B, Figure 8. Pure tin or the alloy before mentioned about the temperature
at which olive oil takes fire is now poured into one of the conduits. The
metal thus poured into the conduit flows down through the empty channel e, e²,
and up into the other conduit. The first conduit is kept full, and as soon as
the metal appears in the second it also is filled to the top by pouring the
metal into it. As soon as both conduits are full a wet cloth is applied to the
outside of the flask A, so as to cool its contents first while the pressure is kept
up by the fluid metal in the conduits. If the metal in the conduits were first
cooled that in the groove e, e, would all be drawn out to supply the deficiency
caused by the shrinking, while by cooling the groove first the final shrinking
takes place in the conduits, and I find the metal has been forced into every
minute pore and crevice between and around the teeth and platinum'pins, and
into the pits, under cuts, and retaining points along the channel e, e, thereby
most effectually securing the teeth to the plate. As soon as the whole
apparatus has sufficiently cooled the composition is carefully removed from
around the teeth, the plate with the conduits attached removed from the
flask, and the gates cut off at the bottom of the brass tubes B, B. The brass
tubes can now be removed from the conduits and the metal melted out of the
latter. I have been for a long time experimenting with this process, and can
say that with anything like reasonable care in conforming to the directions
above given, the success of the operation will be uniform and perfect. The
teeth thus fastened to the plate are attached as perfectly as if they were a part
of the metallic plate itself, and the work is more easily repaired than any other
kind in use. Should the teeth become injured or broken they may be removed
B

page_text: from the plate, and by supplying the broken portion with a new block from
the same mould, and repeating the operation above described, it is rendered as
perfect as before the injury. The same process can also be used for securing
the teeth to lower sets cast in solid gold or silver, thereby securing. weight in a
lower set, which is as great a desideratum as lightness is in an upper set.
What I claim as new and desire to secure by Letters Patent under the
third head of this Invention is,-
1st. The dental plate cast of aluminium or other similar metal having the
recesses E, E, and the channel es, es, behind the teeth when they are in
position, substantially as described.
2ndly. I claim the process above described of forcing melted tin or other
metal around the teeth and platinum pins, as and for the purpose specified.
3rdly. I claim the use of melted tin or any alloy having similar properties
for the purpose of filling the channel or cavity e, e, and attaching the teeth
having platinum pins as for vulcanite work to a metallic plate, as and for the
purpose herein shown and described.
In witness whereof, I, the said Alexander Melville Clark, have hereunto
set my hand and seal, this Fifteenth day of February, in the year of our
Lord One thousand eight hundred and sixty-eight.
A. M. CLARK. (L.S.)