basics of mold making on images.rtf

8/14/2019 Basics of mold making on images.rtf

1/24

Basics of Moldmaking

Introduction

Beginning the mold A one piece poured mold for flat specimens A one piece

poured mold for small specimens Two (or more) part poured molds Layered

molds

A five -layer method for silicone molds Late molds

!acketing !ackets for one-part molds !ackets for multi-part molds

Block making "emolding If it #reaks $inal cleaning %asting in plaster %asting

in polyester

Moldmaking %hecklist

Basics of Moldmaking Introduction

Molds are fre&uently made of fossil specimens' They are made for a variety

of reasons -to share information with others to preserve a specimen in situ

#efore disarticulation and for #lack and white photography' The goal of

moldmaking is to reproduce the information contained in the original detail

as completely as possi#le without damage to the specimen' Bear in mind

that often your cast may #e all that a researcher may see of the specimen' It

is very important then to represent the original as completely as possi#le'

The preparation of a good mold is key to the molding and demolding of

precious fossils with the least amount of harm'

There are two #asic kinds of molds solid poured molds in silicone and thin-

walled molds in either silicone or late' The setup for #oth kinds of molds is

similar as is the rationale for the decisions you will need to make to make a

useful and safe mold' olid molds in silicone are most often used for small

specimens or those without a comple shape' A ma*or consideration in the

use of this kind of mold is cost' A very large solid mold may #e prohi#itively


2/24

epensive' It may also #e difficult to remove a solid and therefore &uite stiff

and unwieldy mass of ru##er from deep undercuts or comple shapes' Large

and comple shapes may re&uire more flei#ility in a mold to make

demolding easier' These re&uire a thin-walled mold of either late or silicone'

+o two molds will #e done in eactly the same way' ,ach specimen is

different and presents different pro#lems' These directions are in several

parts according the type of mold needed' ,ach can #e read independently'

These are only generalied directions' I will try to give the reasons for each

step so that decisions can #e made and directions adapted for each

individual case' .ead through the entire direction #efore #eginning so that

you will #e prepared for upcoming steps' .emem#er that any new

techni&ue will take a while to perfect' If possi#le practice on an easy and

unimportant specimen'

Make sure that the molding process is eplained to the researcher' /utting

consolidants car#owa and molding ru##ers on the specimen can make

un-remova#le changes to the specimen and may preclude certain types of

research later' If you are molding a specimen that #elongs to another

institution make sure that you have written permission to mold the

specimen'

Always make sure that the name and num#er of the specimen and any

other important information are noted #efore you #egin working and that it

is written on the *acket or otherwise noted on the mold' This can prevent

much confusion later'

In addition use care with these materials' .ead the Material "ata afety

heets' 0hile silicone ru##er late ru##er and plaster are fairly harmless

you will want to wear ru##er gloves and an apron' 1se a fume hood when

casting polyester as well as ru##er gloves and an apron' 1se common

sense and care' Any material can #e dangerous if ingested' "on2t eat or

drink while you are working with these materials'

Beginning the mold

3' 3' The first step in the making of any mold is to carefully look at thespecimen' 0ill it stand up to the rigors of the moldmaking process4 0hereare its weak points4 Are there deep recesses (undercuts) that will causetrou#le when demolding or must a#solute fidelity #e sacrificed and shouldthose deep holes #e filled4 If necessary the specimen should #e cleaned andany preparation completed #efore molding' There is no reason to make a


3/24

mold of dirt and ecess glues and consolidants on the specimen' Breaksshould #e repaired and etra glue removed'5' 5' The specimen should then #e coated with a thin #ut complete layerof a consolidant' Two coats of 5-67 Butvar B-89 in acetone are good' Thelayer of consolidant acts to help maintain the specimen and also acts as a

release #etween the molding material and the specimen' Teeth however arenot usually consolidated so as not to interfere with dental wear patternsand other minute details'6' 6' $ossils usually contain many holes small and large that can causetrou#le if the ru##er is allowed to get into them' These holes such asweathering damage foramina and old #reaks need to #e covered yet themold must retain as much information as possi#le' 0hen thought is #einggiven to design of the mold these holes must #e considered' ome deeprecesses may contain important information and so should not #e covered'The mold instead needs to #e designed around them' A good clue as towhich holes must #e filled is to try to see if the hole is #igger on the inside

than the outside' That is is this a small area into which the li&uid ru##er canseep #ut out of which the hardened ru##er cannot #e pulled without#reaking the specimen4

The filler should not cover any more of the #one than is a#solutely necessary'

Thinking of the fossil as information may help guide you' The filling should

not hide any more information than is a#solutely necessary to preserve the

fossil against #reakage' .emem#er that this cast may #e all that a

researcher is a#le to see of this specimen' $illed areas will read in the cast as

solid surfaces that are the same as the rest of the #one' This is why it is

important to keep the filling to the minimum that is needed to preserve thespecimen'

$illing is usually done with %ar#owa' %ar#owa is a common name for

polyethylene glycol' +ot really a wa %ar#owa is solu#le in water making

it easily remova#le from the specimen after molding' %ar#owa comes in a

variety of hardnesses which can #e mied to form a wa that is easily

worka#le' %ar#owa may also #e colored with a tiny #it of powdered

pigment to make it more easily reada#le against the #one' $illing may also

#e done with clay or microcrystalline wa though these are more difficult to

remove after molding' Melted %ar#owa is applied to the hole and when

cool scraped flat with a tool' moothing can #e done with a #rush and

acetone or alcohol' :ery tiny holes can #e filled #y simply scraping a little of

the hard wa into the hole and using acetone to smooth it' The surface of

the filled area is usually slightly #elow the surface of the #one to show as

eactly as possi#le where the filled area #egins'

:ery deep or large apertures can #e stuffed first with slightly dampened


4/24

tissue and a thin layer of filler applied on top' The filler is usually scored or

otherwise marked to distinguish filling from fossil' %are must #e taken to

remove any filling material that is not needed' ;ou can often end up with a

small lump on an important tooth cusp if not careful' A thin layer of

consolidant is applied over the filling'

? to3=


5/24

specimen'@' 9' These molds are almost always made in silicone mied according tomanufacturersC instructions' There are various types of silicone ru##ersmake sure yours has a long enough set time to allow for deairing and a slowpour' After miing the ru##er should #e deaired to prevent the inclusion of

air #u##les in the mold' The cup holding the li&uid ru##er is placed inside avacuum cham#er and all air drawn off' This will cause the material to rise'Make sure there is enough room in the cup for the material to epand to 5-6times its original volume' After the air is removed the material will drop #ackto its original sie and continue to #u##le' It should #e allowed to #u##le forapproimately @-8 minutes for all air to #e eliminated' Allow the air toreturn slowly to the vacuum cham#er and remove the cup'9' 8' The ru##er is slowly poured into the mold from one corner in a smallstream' The pouring should start in an area where there is no #one and theru##er #e allowed to slowly move #y itself over the specimen' It is importantthat the silicone not #e poured in so fast that air cannot escape from

#etween teeth and from small recesses' If there is an area where you are notsure the ru##er has penetrated the ru##er can #e gently pulled #ack with a#rush or needle to allow air holes to fill' Allow the ru##er to set' eemanufacturersC directions this time can #e 9-> hours or longer'8' >' mall molds like these often do not need the support of a *acket' Ifthe mold has thin or large walls or if you feel it would #e #etter if supportedsee !acketing'>' D' After the specimen is *acketed it can #e demolded the specimencleaned and the mold cast' ome molds may have to #e demolded incertain directions to avoid putting stress on raised parts of the specimen' It isuseful to note this in some way on the clay #ed or on the *acket' It is very

difficult to remem#er the eact shape of a #one under a layer of ru##er' ee"emolding $inal cleaning and %asting'

A one piece poured mold for small specimens

3' 3' A one piece mold is usually made when the o#*ect is small or partialsuch as a single tooth or a fragment of *aw' This type of mold is good whenthe specimen is viewed from one side or is relatively conical' .emem#erthat any o#*ect that is molded must also #e removed from the mold' ,venwith a single tooth it may #e necessary to make a more comple mold if itwill endanger the specimen to pull it out of a one piece mold'

5' 5' It is desira#le though not always possi#le to place the o#*ect on asmall platform to create a #ase or a Ehandle? for the specimen' %leansulfur-free (silicone ru##ers react with sulfur inhi#iting cure) clay can #esoftened with a heat lamp' .oll out the clay to form such a #ase which is cutwith a tool to a sie a little larger than the specimen'6' 6' This #ase should then #e placed upon another flat #ed of clay whichwill form the top surface of the finished mold' .emem#er that in terms of themold you are working upside down and in reverse' The cast will reproduce


6/24

what you see'


7/24

avoided' A good place to put a seam is at the edge of an eisting #reak or

along a natural edge in the #one for eample along the top or #ottom of a

ygomatic arch' .emem#er when placing seam lines that there will #e one or

more additional sections of the same mold' ome sections may need to #e

angled in a way that allows the other parts to #e easily worked'

ome thought should #e given as well to casting while designing the mold'

Although consideration of the specimen is most important it must also #e

possi#le to use the mold to make a good cast' ome areas if very thin may

#e difficult to fill with casting material' Fther areas may #e difficult to reach

if they are deeply recessed in the mold' Mold design can help to alleviate

some of these pro#lems'

3' 5' Assuming that you have cleaned and filled the specimen the net

step is to set it up in clay' $ind a clean flat piece of wood that is at5' least 9->G #igger than your specimen' %over with clean paper' Thispiece of wood makes a good sturdy #ase for your work and allows you toturn the work around as needed' %lean sulfur-free clay (silicone ru##ersreact with sulfur inhi#iting cure) can #e softened with a heat lamp and rolledout to the approimate depth of one-half of the specimen' An easy way tomaintain an even thickness of clay is to roll the clay out #etween two sticksof the same depth' These sticks will keep the roller the same height all ofthe way across the clay' If the specimen is large pieces of wood can #e usedto raise the clay #ed to the desired height' The clay #ed should #e largeenough on all sides to allow room for locks walls and with a#out 3=5? to 6=


8/24

where the clay meets the specimen' There will #e another part of the moldfitting right up against this part' eemingly small indentations and lumpscan interfere with the fit of the two parts when casting'3' @' Make sure no ecess clay is on the surface of the specimen' It isuseful to work at this point under a microscope using small needles to

5' clean away undesired clay' Any ecess clay that is not removed will#ecome part of the final cast hiding or disguising information' 1se alcoholand a fine #rush for a final cleaning and smoothing'


9/24

small stream' The pouring should start in an area where there is no #oneand the ru##er #e allowed to slowly move #y itself over the specimen' It isimportant that the silicone not #e poured in so fast that air cannot escapefrom #etween teeth and from small recesses' If there is an area where youare not sure the ru##er has penetrated the ru##er can #e gently pulled #ack

with a #rush or needle to allow air holes to fill' Allow the ru##er to set'5' 33' After the ru##er is set this portion of the mold should #e *acketed'The *acket holds the soft ru##er firmly allowing the parts to #e fit togethertightly' 1sually the top edge of the set ru##er is cut away at a#out a


10/24

tear making it less practical for etremely large molds' Late is very

difficult to tear in fact it may #reak some #ones #efore tearing' An

awareness of the differences of these materials and of the different

re&uirements for different specimens may make it easier to make a

decision as to which material will #e #est in a given situation'

A $ive - Layer Method for ilicone Molds

This method helps ensure a thin even and strong mold wall while minimiing

air #u##les' A thin walled mold is important in molding large or comple

specimens as it allows for the flei#ility necessary to make demolding easier

and less dangerous to the specimen' Ad*ustments can #e made to tailor-

make a mold for a particular specimen for eample a very deep pocket can

#e covered thinly to make it possi#le to remove the mold or a large flat area

can #e covered more thickly to give the mold the necessary rigidity to holdits shape'

3' 3' The set-up for a layered mold is the same as that for Two (or more)part poured molds' After filling holes and cracks with %ar#owa set thespecimen up in a clay #ed with the usual locks' A clay wall approimately3=>? high is placed around the perimeter of the desired mold area that iswhere the ru##er should end' This defines the edge of the mold as well asgiving a guide for the finished thickness of the mold edge' The specimenand the clay are now Etalced? that is talcum powder is #rushed on with asoft #rush and #lown and #rushed off' This thin layer of talc acts as aseparator' The talc should #e removed to the point where it is no longervisi#le ecept as a thin layer when seen under the microscope - if you cansee it there is too much powder left on the specimen'3' 5' 1se a good fairly thin viscosity silicone ru##er that comes with athiotropic agent' ;ou will need #oth thin and thick types of ru##er for this5' process' ome companies make two different thicknesses of siliconethat can #e mied together to make a desired thickness while otherscompanies make an additive which when added to the ru##er causes it tothicken' Mi according to manufacturerCs directions' "o not use a siliconeru##er thinner as this causes the ru##er to tear more easily and to degrademore &uickly'5' 6' Mi only a small amount of thin ru##er -3-5 grams of material willcover a good sied specimen' After miing the ru##er should #e deaired toprevent the inclusion of air #u##les in the mold' The cup holding the li&uidru##er is placed inside a vacuum cham#er and all air drawn off' This willcause the material to rise' Make sure there is enough room in the cup for thematerial to epand to 5-6 times its original volume' After the air is removedthe material will drop #ack to its original sie and continue to #u##le' It


11/24

should #e allowed to #u##le for approimately @-8 minutes for all air to #eeliminated' Allow the air to return slowly to the vacuum cham#er andremove the cup' (An alternative to using a vacuum cham#er is to usepainters Epressure pot? to put the material under pressure and so remove allair from the ru##er')

6'


12/24

smooth the gaue with a spatula as it thickens'9' >' The fifth and usually the final layer is again a slightly thickermiture' The specimen should #y now #e covered evenly with a layerapproimately 3=>? thick' The edge of the mold can #e #rought to the levelof the outer 3=>? high wall' If there are especially thin sections on high

points the silicone miture can #e ad*usted or additional layers placed only inselected spots' This layer serves to smooth the entire surface so that the*acket will release well' It is still important to watch that the mold does not#ecome too thick or #uild up unevenly' A very thick section can causedifficulty and #reakage during demolding' It is #etter to have a thin andeven mold and make #locks to help the *acket lift'3' D' Fn very complicated specimens the ru##er may have to #e pulledoff in certain directions only' $or eample if there is a large protrudingshape which angles toward the front of the specimen' The ru##er may haveto #e5' pulled up from the #ack of the specimen toward the front in order to

prevent #reakage' +otes can #e made or arrows drawn on the *acket toindicate this' It can #e very difficult to remem#er these details after makingseveral parts to a mold and having the specimen o#scured #y layers ofru##er'8' 3' Layered molds are also usually multi-part molds' 0here siliconemeets silicone the parts are separated #y a thin layer of Butvar B-89 andtalc'>' 33' Because of the thinness of the walls of this type of mold a plaster*acket must #e made' Blocks will pro#a#ly #e needed as the thin walls donot fill in most undercuts' ee Block-making !acketing' ee "emolding $inalcleaning and %asting'

Late molds

Late molds are usually made of large specimens where tiny details are not

as important' Late is a natural ru##er and shrinks somewhat on drying'

There are various types of late ru##er' ;ou will want a high solids self-

vulcaniing mold ru##er without ammonia'

3' 3' The specimen is filled and set up as usual' It is sometimes good tospray the specimen with a mold release' Late can #e stored tightly closed

in a wide mouthed *ar'3' 5' 1se a soft #ristle #rush' The #rush will clean up more easily if youdip it into dish detergent and dry it #efore #eginning' Late is painted on tothe specimen in thin layers' "o not paint the late too thickly' Late unlikesilicone ru##er is air dried' Therefore if the ru##er is too thick it will dryunevenly' tart in one section of the specimen and paint fairly &uickly' "onot #rush #ack and forth #ut rather in one direction' If you paint over theru##er as it starts to dry you will pick up the ru##er on your #rush' eep


13/24

painting from wet areas into the unpainted parts of the specimen' Allow thislayer to completely dry' Late will change color as it dries #ecoming moretranslucent' 0hen the entire mold is the same translucent creamy color itis dry' This may take an hour or two' "rying can #e speeded #y using a fan'"o not use heat this can cause the ru##er to shrink dramatically'

5' %lean the #rush with soapy water' Late will pro#a#ly #uild up in the#rush' It can #e removed with a wire #rush' $or larger #rushes make acleaning device #y driving a num#er of small nails through a #oard' crapethe #rush through the nails to clean'6' 6' Late will #e #uilt up in layers' A#out 3 - 35 layers are needed fora medium sied mold and up to 5 for a really large specimen' Make the#rush strokes on succeeding layers in different directions' This will allow aneven #uild up of ru##er' Allow each layer to completely dry #eforeproceeding to the net'


14/24

a#out 3=5 G - @=>G (depending on the sie of the specimen more space isneeded for larger *ackets) cut away the clay #ed which etends away fromthe mold' mooth the clay #ed' 1se :aseline as a separator applying agood #ut fairly thin coat to the entire surface'5' 5' /laster is made usually in a ru##er #owl #y adding plaster to water'

The amount of plaster you will need is dependent on the sie of the mold' $illthe ru##er #owl to no more than 3=5 full of water' Add plaster to the waterslowly sifting it in all around the #owl until it #egins to make islands' That isuntil the plaster has filled the water to *ust a#ove the surface'6' 6' Allow the plaster to sit for a minute for the plaster to #ecome fullysoaked with water' tir the plaster into the water' The mi should #e fairlythick a#out like sour cream or yogurt' More plaster can #e added if the miis too thin' "o not over mi plaster this can affect the hardening'


15/24

smoothed clay #ed' ;ou can use your finger or the round end of a large

#rush to make a num#er of divots into the clay #ed' These will #e the locks

for the *acket' These locks will make all the pieces fit well together without

sliding' They should not have undercuts that can lock the two parts of the

*acket together'

The first part of the *acket is made after the first part of the mold has set in

the same manner as for a one part mold' After that the *acket is treated as if

it were a replacement for the clay #ed' ,ach succeeding part of the *acket is

made up against the previous part' Lift each part of the *acket slightly as

you proceed to ensure that it will release easily when the *acket is finished'

The walls of the parts may have to #e angled so that the pieces do not lock

against each other making it difficult to pull apart the parts of the mold' This

re&uires picturing how the future parts of the mold will fit together'

Multi-part molds often have undercuts' ee Blockmaking'

Block making

Molds made for comple shapes may have deep undercuts or crevasses

even after the ru##er has #een applied' These complicated molds may

re&uire making #locks to fill in undercuts that might cause the *acket to #e

difficult to remove' A #lock usually made of plaster is used to fill in

undercuts with small remova#le pieces which make the surface less irregular'

3' 3' A good way to *udge if #locks will #e needed is to look straight downon the mold from a#ove' This is the way that the *acket will #e lifted off' Tryto picture the *acket #eing lifted straight off the mold and notice if there arerecesses on which the *acket may catch' Those are the undercuts that youwill need to fill'5' 5' Blocks are made in a similar manner to the *acket' :aseline isapplied to the ru##er and slightly thick plaster spatulated into the undercut'6' 6' The surface of the #lock must #e made smooth to prevent catchingof the *acket' This can #e done with the spatula or after the #lock hashardened #y sanding'


16/24

9' 9' After you have made all the #locks needed the *acket may #eprepared as usual' Make sure a good coat of :aseline covers all of the#locks' /laster will tend to stick to itself'

Fther materials may also #e used' $oam ru##er silicone ru##er late

ru##er mied with vermiculite these are only a few' The material usedmatters less than supporting the mold and ena#ling easy removal of the

*acket'

"emolding

"emolding the specimen is the scariest part of moldmaking' This is the time

when it is possi#le to #reak the specimen' reat care must #e taken at this

stage'

"emolding a one part mold

3' 3' After the ru##er has set *acket the specimen if necessary' After the*acket is dry gently remove the *acket' 0ipe off any remaining :aseline orseparator' In a clean area gather together a small spatula alcohol a fine#rush and a #o for the specimen' 0orking slowly around the entire edgeuse the spatula to gently pry up *ust the very edge of the ru##er' !ust loosenthe edge at first' 5' /roceeding around the mold continue lifting' As the mold #egins tolift you can work your fingers under the ru##er to lift it away from thespecimen' It is important to remem#er that you want to pull the ru##er away

from the specimen e&ually in all directions to avoid putting stress on any onespot' This is particularly true in thin areas' The ru##er should #e lifted upfrom #oth sides'3 ome molds may have to #e demolded only in certain directions toavoid putting stress on raised parts of the specimen' It is useful to note thisin some way on the clay #ed or on the *acket' It is very difficult to remem#erthe eact shape of a #one under a layer of ru##er'5' 6' If the ru##er seems to want to stick to the specimen apply a littlealcohol with the #rush to the edges of the ru##er where it is in contact withthe mold' 0orking under the microscope can help you to see how the ru##eris lifting'

6'


17/24

@' 9' %heck the mold for air #u##les and for any #roken pieces of thespecimen' %heck the specimen for #reaks and return it to its #o'

"emolding two (or more) part molds

This is similar to demolding one part molds' "emold one part at a timeallowing the other parts to remain supported #y the *acket until you are

ready to demold them' ometimes multi-part molds will need to #e

demolded in a certain order' This can #e noted on the *acket'

If it #reaks

If the specimen #reaks don2t panic' This is why glue was invented' ome

#reaks can #e glued together with Acryloid B85 or Butvar B89 in the mold'

The adhesive will not stick to the mold' Ftherwise carefully remove allpieces and place them in a clean #o' .emove all of the specimen from the

mold' %arefully look over the specimen for any other #reaks or loose pieces'

.eassem#le any #reaks without glue first it is sometimes necessary to put

one piece #ack first #efore others can #e *oined' Also some pieces may fit in

a way that #locks others' By fitting the pieces together dry you can decide

how to proceed' 1se thick Butvar or B-85 Acryloid as a glue' ;ou want a

glue that is easily remova#le in case pieces need to #e moved'

$inal %leaning

pecimens that have #een molded should #e as clean or cleaner than they

were originally' After the specimen has #een safely removed from the *acket

it is important to clean it right away #efore returning it to the collection'

Acryloid or Butvar can #e removed with alcohol or acetone' %lay and wa

must #e gently removed with a needle and cleaned with a #rush and either

alcohol or acetone' %ar#owa dissolves in water' .emove as much as

possi#le first with a needle and use a #rush with water to remove the

remainder' $or specimens in water solu#le matri use alcohol to remove the

%ar#owa'

Make sure the num#er and any other pertinent information is in place on the

specimen'

%asting in plaster

/laster is easier to cast than polyester resin #ut will not have the &uality of


18/24

detail that a resin can capture' In addition plaster will #e opa&ue' Most

#one is slightly translucent' It is difficult to color plaster #efore miing' It is

#etter to have white cast and paint it in the desired manner later' Before

painting a plaster cast put two or three thin coats of Butvar on the cast and

allow it to completely dry' This will keep the paint from soaking into the cast'

3' 3' After the mold is finished the *acket made and the specimenremoved and cleaned the mold should #e well cleaned with alcohol using aclean lint free rag' The cleaning removes any traces of separator and anydirt left from the specimen' The mold should then #e left for 3-5 days for theru##er to completely cure' If you are casting into a silicone mold no specialmold preparation is necessary' If you are casting into a late mold spray themold with mold release'5' 5' /laster is made usually in a ru##er #owl #y adding plaster to water'The amount of plaster you will need is dependent on the sie of the mold' $ill

the ru##er #owl to no more than 3=5 full of water' Add plaster to the waterslowly sifting it in all around the #owl until it #egins to make islands' That isuntil the plaster has filled the water to *ust a#ove the surface'6' 6' Allow the plaster to sit for a minute for the plaster to #ecome fullysoaked with water' tir the plaster into the water' The mi should not #e toothick a#out like melted ice cream' More plaster can #e added if the mi istoo thin' "o not over mi plaster this can affect the hardening'


19/24

A neutral medium grey is the most commonly used color here for making

scientific research casts' This color shows the detail well and photographs

well also'

%asts can #e colored any other #onelike color for display purposes' %asts for

display are usually painted as to resem#le the real o#*ect as closely as

possi#le in order to give the viewer a feeling for the real o#*ect'

3' 3' After the mold is finished the *acket made and the specimenremoved and cleaned the mold should #e well cleaned with alcohol using aclean lint-free rag' The cleaning removes any traces of separator and anydirt left from the specimen' The mold should then #e left for 3-5 days for theru##er to completely cure'5' 5' %olors can #e mied at any time #efore casting' If you are making a

display cast generally mi the color to match the lightest color in the fossilthat you are reproducing' The ratio of color to resin should #e no more than@7' 0hile sometimes you can get away with a little more color too muchcolor interferes with the setting of the resin' enerally all colors will havesome talc or other thickener mied in as well' This can affect the color' Thethickener can #e added when the color is mied and the mi catalyed later'%atalye to the original weight not the weight that includes the thickener' 6' /FL;,T,. .,I+ A+" T, %ATAL;T A., +FJIF1 MAT,.IAL'Always work in the fume hood and wear ru##er gloves and an apron' Becareful of #reathing the dust from hardened resin and also of #reathing in thetalc or %a#-F-il powders' /olyester can #e stored in a tightly closed

3 glass or nalgene *ar and kept in a flamma#le li&uid storage ca#inet'eep the catalyst separate'6'


20/24

and shrinks more if it #ecomes hot' /olyester resin creates heat during the

chemical reaction which makes it set' If the material is too thick the heat

generated can cause the cast to shrink or in etreme cases can cause the

cast to crack' Therefore resin should as a rule not #e more then 3=< -3=5G

thick for each layer'

.emem#er that you can always make more'

3' 8' Add the catalyst to the resin' The ratio is 5-67 of catalyst to resin'That is if you make 3 grams of resin you will add 5-6 grams of catalyst for3 grams of resin you will add '5-'6 grams of catalyst' Mi catalyst into resinwell' The catalyst is colorless and as you are adding &uite small amountsmiing well #ecomes important' Miing in a pattern is the easiest scrapingthe sides and the corners of the cup well'5' >' 1sing a #rush of the appropriate sie paint a thin layer of mied

material into the mold' Make sure to paint it in thinly do not allow large#lo#s of material to gather in corners' This can cause air #u##les on the

finished cast' 1se a spatula to clean the edges of the mold' ;ou will need to

keep the edges of the mold very clean until the final layer'

%lean the #rush and the spatula with acetone' eep the cup in the hood until

the resin has completely hardened'

Allow this layer to gel' This will take a#out 5-6 minutes or up to an

hour depending on the catalyst itCs age and the weather'

.esin like plaster thickens as it sets' ;ou will have 3 -3@ minutes in

which to work' ome very large molds may re&uire 5 or more miings of

resin' .emem#er that you can always make more'

3' D' A second layer is applied in the same way and allowed to gel'5' 3' The third layer should #e thickened with talc %a#-F-il or someother dry thickener and again painted in' The edges should #e cleaned aftereach layer'

3' 33' The num#er of layers needed depends on the sie of the mold':ery large molds need the addition of fi#erglass strand or mat for etrastrength' The additional layers should #uild up the walls of the castespecially on the edges'5' $i#erglass is added in the following manner' /aint a layer of fairly thinpolyester into the mold' Add the fi#erglass and using more polyester &uicklytamp down the fi#erglass with a #rush to thoroughly impregnate the fi#erwith resin' ;ou can use more resin to smooth the fi#erglass' Make the


21/24

miture a#out 57 so that it is slower to gel'6' 35' If you are making a one piece mold the mold can #e finishedwhenever the layers are #uilt up to a sturdy thickness approimately 3=>GG' /ut good #ead of resin all around the edges ofthe mold' This will glue together the seams' /ut the parts of the moldtogether and #and tightly with ru##er #ands'6' 36' Allow the mold to set at least overnight for the resin to completelycure' /olyester resin doesn2t completely cure on the side that is against themold' This can result in a shiny appearance in the cast' A more completecure can #e achieved #y further drying the mold in the oven at a very lowheat for a#out an hour' This can #e important for research casts where acompletely matte appearance is desired'


22/24

9' Lay the specimen on the clay #ed and draw a line with apoint into the clay marking the edges of the specimen' %uthole out along that line' "rop the specimen in to the clay#ed up to the seam line' 1se small #its of clay to prop upthe specimen where needed so that the edge of the clay

#ed is approimately even with the seam line' 1se soft clayto #uild up the #ed where necessary or cut away the clay#ed if the seam line dips lower' More clay is used to fill inthe clay #ed right up to the specimen'

8'mooth the entire surface of the clay especially along theseam line' +o small holes should #e left for ru##er to seepthrough' 1nder the microscope smooth clay right at theseam line'

>' 1se alcohol and a fine #rush for a final cleaning and

smoothing'D' .oll out a rod of clay approimately 3=


23/24

36'/our the ru##er slowly into the mold from one corner in asmall stream' The pouring should start in an area wherethere is no #one and the ru##er #e allowed to slowly move#y itself over the specimen' Allow the ru##er to set'

3


24/24

5

basics of mold making on images.rtf

Documents