Plastic polymers can settle out, probably because they are heavier, and
settle to bottom of container.  I always stir my embedding media, agitation
in processors probably does a good mix there.  Just go to a grocery store
and by a long spatula, or large cooking spoon, pancake turner, and stir
away to redistribute polymers BEFORE embedding.  My embedding center has a
rubber spatula (refugee from home cooking utensils) flat, wide and cheap.  

I never have melted paraffin sitting around that long, I worry that the
heat will change additives, polymers are just one of many.  Have had
paraffin turn yellow, and smell bad, this was tossed, and I always melt
close to melting point unless mfr says it is ok to go higher than M.P. 

You are not being overly cautious, in fact, nice technic!! Bet your tissues
section nicely!?? 

There was an excellent article in J Histotechnology years back about
problems with Paraplast, water contamination, etc by Maria Wynchuck. I
would have to look it up.  I used to get water droplets in Paraplast Plus,
but it is colder here in winter, and I think it was water condensation (in
embedding center, never saw this in processing). 

 





At 02:46 PM 10/5/01 -0500, you wrote:
>I have heard from other techs that embedding paraffin (Paraplast, among
>others) tends to have some problems with stability. Some say that the
>plastic
>polymers will settle out and you need to stir it before using.  Also if you
>keep it melted a long time  (not specified) that these polymers will
>evaporate out and you loose there advantage in cutting.  ( note: this is
>said to happen even if the temperature is kept at the proper level for the
>type of paraffin.) We go through a lot of paraffin, so there is new in the
>dispenser about every other day and we check the temp every day too.  I
>stir it before dispensing, this is kind of difficult in the embedding
>station, but can be done.  Has anyone heard of or had problems that could be
>related to this? Are we just being over cautious?
>
>thanks,
>PS  Sorry if you received message twice, I was not sure it was sent.
>
>Rose Richardson
>Senior Research Technologist
>Lab Phone: 317-274-1591
>
>
>
>
Gayle Callis
MT,HT,HTL(ASCP)
Histopathology Supervisor
Veterinary Molecular Biology - Marsh Lab
Montana State University - Bozeman
19th and Lincoln St
Bozeman MT 59717-3610

406 994-6367
406 994-4303 (FAX)